Welding material and welded joint structure

ABSTRACT

A welding material, to be used for welding a base metal made of an austenitic alloy comprising C≦2.0%, Si≦4.0%, Mn: 0.01 to 3.0%, P: more than 0.03% to not more 0.3%, S≦0.03%, Cr: 12 to 35%, Ni: 6 to 80%, sol. Al: 0.001 to 1% and N≦0.3%, with the balance being Fe and impurities to a base metal made of another austenitic alloy, which comprises C: more than 0.3% to 3.0%, Si≦4.0%, Mn≦3.0%, P≦0.03%, S≦0.03%, Cr: more than 22% to 55%, Ni: more than 30% to not more than 70%, sol. Al: 0.001 to 1% and N≦0.3%, with the balance being Fe and impurities can suppress the weld solidification cracking which occurs in an austenitic alloy having a high P content and showing fully austenitic solidification. Therefore, the said welding material can be widely used in such fields where a welding fabrication is required. The said welding material may contain a specific amount or amounts of one or more elements selected from Cu, Mo, W, V, Nb, Ti, Ta, Zr, Hf, Co, B, Ca, Mg and REM.

TECHNICAL FIELD

The present invention relates to a welding material and a welded jointstructure. Particularly, it relates to a welding material to be used inwelding austenitic alloys and to an austenitic alloy welded jointstructure. More particularly, the present invention relates to a weldingmaterial which can be used in welding both austenitic alloys having ahigh P content or, further, in welding two austenitic alloys, differentin kind, namely an austenitic alloy having a high P content and anaustenitic alloy having a low P content (hereinafter also referred to as“dissimilar material welding”) and which is excellent in weldsolidification cracking resistance. The present invention also relatesto a welded joint structure which can be widely applied to a steel pipeor steel plate and so on in which fields where creep strength andcorrosion resistance are required and which is excellent in weldsolidification cracking resistance or not only in weld solidificationcracking resistance but also in ductility.

BACKGROUND ART

Austenitic stainless steels, for example, such as SUS 304, SUS 316 andSUS 310S and others, which are regulated in JIS G 4304 (2005), are knownto be materials containing Cr and Ni as main elements and also excellentin corrosion resistance.

And, it is known that when austenitic steels contain P, which isessentially an impurity element, at high concentration levels, Pcontributes toward precipitation hardening by making M₂₃C₆ carbidesfiner, hence lead to improvements in high temperature strengthcharacteristics, typically creep strength, as shown in the PatentDocuments 1 to 4.

Similarly, the Patent Document 5 proposes an austenitic stainless steelmarkedly improved in high temperature strength characteristics,typically creep strength, as a result of its containing P at a highconcentration level.

The Patent Document 6 and the Patent Document 7 disclose metallicmaterials which contain P at a level of exceeding 0.05% and contributeimprovements in the metal dusting resistance of base metals.

The Patent Document 8 also discloses a welded joint and a weldingmaterial which is excellent in metal dusting resistance and is reducedin susceptibility to weld solidification cracking as a result of theircontaining Ti, at an appropriate level, which is based on a relationshipbetween the contents of Si and Cu.

Further, the Patent Document 9 discloses, as a welding material foraustenitic alloys, a welding material for a gas shielded arc weldingwhich is reduced in susceptibility to solidification cracking byimposing the following restrictions on the contents of P and S asimpurities: “P: not more than 0.01% and P+S: not more than 0.02%”. ThePatent Document 10 discloses a method of welding high Cr and high Nialloy members while inhibiting weld solidification cracking in which themethod comprises using a welding material containing Nb in addition tothe composition of the base metal members.

The Patent Document 11 discloses a high C and a high Cr-high Ni typewelding material which is so constituted that a Cr—Ni containing alloyplate suitable for wire drawing is used as a sheath material, in which ahigh C and high Cr alloy powder is covered to form a base wire material.

Further, the Patent Document 12 discloses a welded joint, excellent inresistance to high temperature cracking in welding, and characterized inthat the weld metal satisfies two formulas. The quantity of theinclusions, which include P, the weld metal is regulated to 0.01 to 0.1%in terms of the area ratio so that the problem of hot crackingencountered in the dissimilar material welding of SUS 304 to invar alloy(36 Ni and the balance is Fe) may be overcome.

However, since P is hardly soluble in the austenite, P causes markedincreases in the susceptibility to weld solidification cracking to alarger extent, not only in the case that a primary crystal austenitesolidification occurs but also particularly in the case that a fullyaustenitic solidification occurs.

The said weld solidification cracking occurs when the liquid phase,which exists among dendrites during weld solidification and remains in afilmy form in low temperature regions, and cannot withstand the appliedstress.

An increased P content results in an increase in the susceptibility toweld solidification cracking. This is due to P being markedlyconcentrated in the liquid phase during solidification and thereforegreatly lowers the solidification completion temperature of the liquidphase and thus the liquid phase remains in low temperature regions.Therefore, for example in the Non-Patent Document 1, it is shown thatthe P content should be rigidly restricted.

Consequently, in the present state of affairs, the restraints areimposed on the P content in stainless steels and Ni based alloys whichshow fully austenitic solidification. For example, in the case of SUS310S which is a steel species representative of the above-mentionedaustenitic stainless steels, shows the fully austenitic solidificationand is regulated in JIS G 4304 (2005), the content of P is restricted tonot more than 0.045%. The welding material to be used in welding thesaid SUS 310S, the content of P is restricted to a lower level, that isto say, not more than 0.030%, in JIS G 4316 (1991) from the viewpoint ofthe said weld solidification cracking.

That is to say, in spite of the fact that P is so far known to producefavorable effects on the characteristics of austenitic steels, improvinghigh temperature strength, typically creep strength, and improvingcorrosion resistance and so on, the content thereof has so far beenrestricted since it markedly increases their susceptibility to weldsolidification cracking.

Patent Document 1: JP 37-17113 A

Patent Document 2: JP 62-243742 A

Patent Document 3: JP 62-243743 A

Patent Document 4: JP 62-267454 A

Patent Document 5: WO 2006/106944

Patent Document 6: JP 2007-186727 A

Patent Document 7: JP 2007-186728 A

Patent Document 8: JP 2006-45597 A

Patent Document 9: JP 7-60481 A

Patent Document 10: JP 9-52194 A

Patent Document 11: JP 11-285890 A

Patent Document 12: JP 2001-18089 A

Non-Patent Document 1: Y. Arata, F. Matsuda and S. Katayama:Transactions of JWRI, Vo. 6-1 (1977), pp. 105 to 116

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

As for the invention disclosed in the above-mentioned Patent Document 1,there is no description of the marked increase in the susceptibility toweld solidification cracking due to an excessive content of P.Therefore, it is very difficult to use the steel disclosed therein as asteel which is required to be welded.

As for the inventions disclosed in the Patent Documents 2 to 4 as well,P is added only to produce improving effects of high temperaturecharacteristics and, although the malignant influence of an excessiveaddition of P is described, there is no description at all of anytechnique for reducing the susceptibility to the weld solidificationcracking of austenitic stainless steels which show the fully austeniticsolidification in the stage that the austenite solidifies as a primarycrystal.

In the Patent Document 5, the weldability of base metals in theVarestraint test is taken into consideration, but no welding materialand welded joint structure is considered.

In the Patent Document 6 and the Patent Document 7, there is noconsideration to a marked increase in the susceptibility tosolidification cracking on the occasion of welding resulting from anincrease in P content. In the Patent Document 8 as well, only theresults of investigations at the conventional low P content levels aredisclosed.

The inventions disclosed in the Patent Document 9 and the PatentDocument 10 are not directed to welding materials for welding metallicmaterials which contain high P concentrations. The base metal which isdisclosed in the example of the Patent Document 11 has a low andinsignificant P content.

In the example of the Patent Document 12, there are shown only theresults of the welding of alloys which mutually have identicalcompositions and, further, weld cracking is inhibited only in the casewhere austenitic alloys, having an alloy composition containing P at acontent level of at most 0.030%, are used.

As described above, in all the Patent Documents 1 to 12, there is noconsideration for welding materials and welded joint structures whichare capable of inhibiting weld cracking in welding using alloys whichhave a high P content as base metals.

In the actual welding fabrication, not only welding using austeniticalloys having a high P content as base metals but also dissimilarmaterial welding using materials differing in composition, for example,an austenitic alloy having a high P content and an austenitic alloyhaving a low P content as base metals is anticipated. However, in any ofthe above-mentioned Patent Documents 1 to 12, such dissimilar materialwelding is not considered.

P is an element which can improve high temperature strengthcharacteristics, in particular creep strength, and corrosion resistance.Therefore, if a technique is obtained by which the susceptibility toweld solidification cracking of austenitic alloys which show the fullyaustenitic solidification on the occasion of welding can be reduced,such a technique will be expected to contribute toward developingaustenitic alloys, which are economically advantageous and highfunctional, by utilizing P which is an inexpensive element.

Further, from the viewpoint of the welded joint structure, it oftenbecomes necessary for the weld metal to reliably have ductility as aperformance characteristic of the welded portion. This is due to, whenthe weld metal has a very hard microstructure and is low in ductility, abending fabrication may cause a rupture during the treatment, renderingit difficult to use the welded structure for its intended use, even ifno solidification cracking is observed.

The present invention has been accomplished in view of theabove-mentioned state of affairs. It is an objective of the presentinvention to improve the weldability of austenitic alloys which have ahigh P content and also show fully austenitic solidification (in otherwords, austenitic alloys which have a fully austenitic microstructure),in particular to reduce the susceptibility of those alloys to weldsolidification cracking, which is the most important problem they mayencounter. More specifically, the objective of the present invention isto provide a welding material for welding austenitic alloys whichenables welding with excellent weld solidification cracking resistance,even when at least one of the base metal austenitic alloys to be weldedhas a high P content and also shows fully austenitic solidification, aswell as the austenitic alloy welded joint structure resulting fromwelding of austenitic alloy base metals using the said welding material.

Another objective of the present invention is to provide an austeniticalloy welded joint structure as mentioned above which not only reducesthe susceptibility to weld solidification cracking but also hasexcellent ductility.

Means for Solving the Problems

As already mentioned hereinabove, in spite of the fact that P is so farknown to produce favorable effects on the characteristics of austeniticsteels, improving high temperature strength, typically creep strength,and improving corrosion resistance and so on, the content thereof has sofar been restricted since it markedly increases their susceptibility toweld solidification cracking.

On the occasion of welding of such austenitic alloys containing a highconcentration of P as base metals, even if the welding is carried outusing a welding material having a low P content, the ratio of dilutionfrom the base metals is high in the weld metal of the primary layer.Therefore, P in the base metals flows into the weld metal, causing the Pcontent therein to arrive at a level exceeding the upper limit of 0.03%for ordinary materials, with the result that the occurrence ofsolidification cracking in the weld metal can hardly be avoided.

Therefore, the present inventors made various investigations in searchof a technique for reducing the susceptibility to weld solidificationcracking and also a technique for causing the weld metal to ensure highductility on the occasion of the so-called “similar material welding”using, as base metals, alloys containing P in similarly highconcentrations and showing the fully austenitic solidification as wellas on the occasion of “dissimilar material welding” using, as basemetals, alloys differing in P content. As a result, the followingfindings (a) to (j) were obtained.

(a) When austenitic alloys having a high P content are welded together,P is concentrated in the liquid phase of a single-layer welding or atleast the primary layer in a multi-layer welding where the ratio ofdilution from the base metals is high and, as a result, thesusceptibility to solidification cracking is increased.

(b) In the case of dissimilar material welding, that is to say, in thecase of the welding of the austenitic alloy having a P contentrestricted to a level for ordinary steel materials, namely 0.03% orbelow, to another base metal having a high P content, P flows into theweld metal to increase the P concentration in the liquid phase and, inthe weld metal of the primary layer, in particular, the susceptibilityto weld solidification cracking increases compared with the case wherematerials each having an ordinary P content level are welded together.

(c) When the C content in the weld metal is increased and, at the sametime, a high Cr content not less than a specific level is secured, the“M₇C₃” type eutectic carbides, which are stable at high temperaturesduring weld solidification can be effectively utilized to promote thereduction of the entropy of the system and, thus, the progress ofsolidification can be accelerated.

(d) Even when the susceptibility to weld solidification cracking isincreased due to an increase in the P concentration in the liquid phaseon the occasion of similar or dissimilar material welding, using analloy or alloys having a high P content, as mentioned above under (a)and (b); if the progress of solidification is thermodynamicallyaccelerated, the time in a region in which a small amount of liquidphase, which is low in ductility and serves as a starting point forsolidification cracking remains is shortened and, as a result,solidification cracking is inhibited.

(e) Therefore, in order to counteract the malignant influence of anincrease in the P content in the weld metal caused by the flowing of Pfrom the base metal, it is desirable to use a welding material having ahigh C content and a high Cr content.

(f) In the case of a single-layer welding or the primary layer of amulti-layer welding, the ratio of dilution from base metals is high, asmentioned above under (a). Accordingly, when the P content in the basemetal is high, P flows into the weld metal to cause an increase in Pconcentration in the liquid phase, so that the susceptibility to weldsolidification cracking increases as compared with the welding ofordinary P content, that is not more than 0.03%. Therefore, weldsolidification cracking can be inhibited by using a welding materialhaving a high C content and a high Cr content, at least in the primarylayer, and selecting the welding conditions so that at least the weldmetal of the primary layer may have a composition within a specificrange. Furthermore, the level of strength required for the welded jointstructure can be secured and a sound bead shape can be obtained byselecting the penetration bead height in a specific range.

(g) On the other hand, when a welded joint structure is built up bycarrying out a single-layer welding or a multi-layer welding, using awelding material having an excessively high C content, coarse eutecticcarbides, which are low in ductility crystallize out in excess in theweld metal and the elongation and the reduction of area of the weldmetal are markedly reduced, therefore excellent ductility cannot beensured.

(h) Therefore, in the case of creating welded joint structures by amulti-layer welding, in particular, the use of a high-Cr weldingmaterial containing C at a level which exceeds 0.6%, at least in theprimary pass of the multi-layer welding, makes it easy to suppress theweld solidification cracking. In the second and subsequent build-uppasses of the multi-layer welding, the amount of P flowing into the weldmetal is relatively suppressed. Therefore, the use of a high-Cr weldingmaterial having a C content lowered compared with the occasion in theprimary pass welding, namely a C content of more than 0.2% to not morethan 0.6%, makes it possible to reduce the amount of eutectic carbidescrystallizing out and thereby bring about improvements in ductility.Accordingly, when the primary pass welding and the subsequent build-uppasses of the multi-layer welding are carried out in the mannermentioned above, the weld solidification cracking, not only in theprimary pass of the multi-layer welding but also in the subsequentbuild-up passes thereof can be inhibited. Further, welded jointstructures having excellent ductility can be obtained.

(i) On the other hand, when the primary pass welding is carried outunder welding conditions in which the ratio of dilution from the basemetals is less than 50%, the amount of P flowing into the weld metal issuppressed. Therefore, even when a high-Cr welding material with alowered C content, namely a C content of more than 0.2% to not more than0.6%, is used under such welding conditions as mentioned above, itbecomes possible to inhibit the occurrence of weld solidificationcracking and provide welded joint structures which have reliableexcellent ductility.

(j) In the case of producing welded joint structures by a multi-layerwelding; if the welding is carried out, at least in the primary passwelding, under welding fabrication conditions in which the ratio ofdilution from the base metals is lower than 50%, and the amount of Pflowing into the weld metal in the primary layer is reduced, comparedwith the case (g) mentioned above. Therefore, if the welding of alllayers, inclusive of the primary layer, is carried out using a high-Crwelding material having a C content of more than 0.2% to not more than0.6%, the amount of eutectic carbides crystallizing out can be reducedand improvements in ductility can be brought about. And, in this case,not only the weld solidification cracking in the primary pass of themulti-layer welding can be prevented by the control of the ratio ofdilution from the base metals but also the weld solidification crackingin the subsequent build-up passes thereof can be inhibited and, further,welded joint structures having excellent ductility can be obtained.

The present invention has been accomplished on the basis of theabove-described findings. The main points of the present invention arethe welding materials shown in the following (1) to (3), and the weldedjoint structures shown in the following (4) to (12).

(1) A welding material to be used for welding a base metal made of anaustenitic alloy having the following “chemical composition 1” to a basemetal made of another austenitic alloy, comprising:

by mass percent, C: more than 0.3% to not more than 3.0%, Si: not morethan 4.0%, Mn: not more than 3.0%, P: not more than 0.03%, S: not morethan 0.03%, Cr: more than 22% to not more than 55%, Ni: more than 30% tonot more than 70%, sol. Al: 0.001 to 1% and N: not more than 0.3%, withthe balance being Fe and impurities:

“Chemical composition 1”: A chemical composition which comprises, bymass percent, C: not more than 2.0%, Si: not more than 4.0%, Mn: 0.01 to3.0%, P: more than 0.03% to not more than 0.3%, S: not more than 0.03%,Cr: 12 to 35%, Ni: 6 to 80%, sol. Al: 0.001 to 5% and N: not more than0.3%, with the balance being Fe and impurities.

(2) The welding material according to the above (1), in which the basemetal made of the another austenitic alloy has the following “chemicalcomposition 1or 2”:

“Chemical composition 1”: A chemical composition which comprises, bymass percent, C: not more than 2.0%, Si: not more than 4.0%, Mn: 0.01 to3.0%, P: more than 0.03% to not more than 0.3%, S: not more than 0.03%,Cr: 12 to 35%, Ni: 6 to 80%, sol. Al: 0.001 to 5% and N: not more than0.3%, with the balance being Fe and impurities:

“Chemical composition 2”: A chemical composition which comprises, bymass percent, C: not more than 2.0%, Si: not more than 4.0%, Mn: 0.01 to3.0%, P: not more than 0.03%, S: not more than 0.03%, Cr: 12 to 35%, Ni:6 to 80%, sol. Al: 0.001 to 5% and N: not more than 0.3%, with thebalance being Fe and impurities.

(3) The welding material according to the above (1) or (2), in which oneor more alloys among the base metals and welding material contain one ormore elements selected from the first group and the second group or bothgiven below in lieu of a part of Fe, by mass percent:

First group: Cu: not more than 5%, Mo: not more than 10%, W: not morethan 10%, V not more than 2%, Nb: not more than 3%, Ti: not more than3%, Ta: not more than 8%, Zr: not more than 1%, Hf: not more than 1%,Co: not more than 15% and B: not more than 0.03%; and

Second group: Ca: not more than 0.05%, Mg: not more than 0.05% and REM:not more than 0.3%.

(4) A welded joint structure in which the base metal according to anyone of the above (1) to (3) is welded by using the welding materialaccording to any one of the above (1) to (3).

(5) A welded joint structure which is constructed with base metals eachmade of an austenitic alloy comprising, by mass percent, C: not morethan 2.0%, Si: not more than 4.0%, Mn: 0.01 to 3.0%, P: more than 0.03%to not more than 0.3%, S: not more than 0.03%, Cr: 12 to 35%, Ni: 6 to80%, sol. Al: 0.001 to 5% and N: not more than 0.3%, with the balancebeing Fe and impurities, and a weld metal made of an austenitic alloyhaving the following characteristics (i) and (ii):

(i) the chemical composition of at least the primary layer being weldedfrom one side, comprises, by mass percent, C: more than 0.1% to not morethan 0.7%, Si: not more than 4.0%, Mn: not more than 3.0%, P: more than0.03% to not more than 0.1%, S: not more than 0.03%, Cr: 18 to 30%, Ni:more than 10% to not more than 70%, sol. Al: 0.001 to 1% and N: not morethan 0.3%, with the balance being Fe and impurities; and

(ii) the penetration bead has a height of 0 to 3 mm.

(6) The welded joint structure according to the above (5), in which oneor more alloys among the base metals and weld metal contain one or moreelements selected from the first group and the second group or bothgiven below in lieu of a part of Fe, by mass percent:

First group: Cu: not more than 5%, Mo: not more than 10%, W: not morethan 10%, V: not more than 2%, Nb: not more than 3%, Ti: not more than3%, Ta: not more than 8%, Zr: not more than 1%, Hf: not more than 1%,Co: not more than 15% and B: not more than 0.03%; and

Second group: Ca: not more than 0.05%, Mg: not more than 0.05% and REM:not more than 0.3%.

(7) A welded joint structure resulting from welding of a base metal madeof an austenitic alloy having the following “chemical composition 1” toa base metal made of another austenitic alloy, on the occasion ofwelding, a welding material which comprises, by mass percent, C: morethan 0.6% to not more than 2.0%, Si: not more than 4.0%, Mn: not morethan 3.0%, P: not more than 0.03%, S: not more than 0.03%, Cr: more than22% to not more than 35%, Ni: more than 30% to not more than 70%, sol.Al: 0.001 to 1% and N: not more than 0.3%, with the balance being Fe andimpurities, is used in the primary pass of the multi-layer welding and awelding material which comprises, by mass percent, C: more than 0.2% tonot more than 0.6%, Si: not more than 4.0%, Mn: not more than 3.0%, P:not more than 0.03%, S: not more than 0.03%, Cr: more than 22% to notmore than 35%, Ni: more than 30% to not more than 70%, sol. Al: 0.001 to1% and N: not more than 0.3%, with the balance being Fe and impurities,is used in the subsequent build-up passes of the said multi-layerwelding:

“Chemical composition 1”: A chemical composition which comprises, bymass percent, C: not more than 2.0%, Si: not more than 4.0%, Mn: 0.01 to3.0%, P: more than 0.03% to not more than 0.3%, S: not more than 0.03%,Cr: 12 to 35%, Ni: 6 to 80%, sol. Al: 0.001 to 5% and N: not more than0.3%, with the balance being Fe and impurities.

(8) The welded joint structure according to the above (7), in which thebase metal made of the another austenitic alloy has the following“chemical composition 1or 2”:

“Chemical composition 1”: A chemical composition which comprises, bymass percent, C: not more than 2.0%, Si: not more than 4.0%, Mn: 0.01 to3.0%, P: more than 0.03% to not more than 0.3%, 5: not more than 0.03%,Cr: 12 to 35%, Ni: 6 to 80%, sol. Al: 0.001 to 5% and N: not more than0.3%, with the balance being Fe and impurities:

“Chemical composition 2”: A chemical composition which comprises, bymass percent, C: not more than 2.0%, Si: not more than 4.0%, Mn: 0.01 to3.0%, P: not more than 0.03%, S: not more than 0.03%, Cr: 12 to 35%, Ni:6 to 80%, sol. Al: 0.001 to 5% and N: not more than 0.3%, with thebalance being Fe and impurities.

(9) The welded joint structure according to the above (7) or (8), inwhich one or more alloys among the base metals and welding materialcontain one or more elements selected from the first group and thesecond group or both given below in lieu of a part of Fe, by masspercent:

First group: Cu: not more than 5%, Mo: not more than 10%, W: not morethan 10%, V: not more than 2%, Nb: not more than 3%, Ti: not more than3%, Ta: not more than 8%, Zr: not more than 1%, Hf: not more than 1%,Co: not more than 15% and B: not more than 0.03%; and

Second group: Ca: not more than 0.05%, Mg: not more than 0.05% and REM:not more than 0.3%.

(10) A welded joint structure resulting from welding of a base metalmade of an austenitic alloy having the following “chemical composition1” to a base metal made of another austenitic alloy, on the occasion ofwelding, using a welding material which comprises by mass percent, C:more than 0.2% to not more than 0.6%, Si: not more than 4.0%, Mn: notmore than 3.0%, P: not more than 0.03%, S: not more than 0.03%, Cr: morethan 22% to not more than 35%, Ni: more than 30% to not more than 70%,sol. Al: 0.001 to 1% and N: not more than 0.3%, with the balance beingFe and impurities, at least the welding of the primary layer is carriedout under a condition such that the ratio of dilution from the basemetals becomes less than 50%:

“Chemical composition 1”: A chemical composition which comprises, bymass percent, C: not more than 2.0%, Si: not more than 4.0%, Mn: 0.01 to3.0%, P: more than 0.03% to not more than 0.3%, S: not more than 0.03%,Cr: 12 to 35%, Ni: 6 to 80%, sol. Al: 0.001 to 5% and N: not more than0.3%, with the balance being Fe and impurities.

(11) The welded joint structure according to the above (10), in whichthe base metal made of the another austenitic alloy has the following“chemical composition 1or 2”:

“Chemical composition 1”: A chemical composition which comprises, bymass percent, C: not more than 2.0%, Si: not more than 4.0%, Mn: 0.01 to3.0%, P: more than 0.03% to not more than 0.3%, S: not more than 0.03%,Cr: 12 to 35%, Ni: 6 to 80%, sol. Al: 0.001 to 5% and N: not more than0.3%, with the balance being Fe and impurities:

“Chemical composition 2”: A chemical composition which comprises, bymass percent, C: not more than 2.0%, Si: not more than 4.0%, Mn: 0.01 to3.0%, P: not more than 0.03%, S: not more than 0.03%, Cr: 12 to 35%, Ni:6 to 80%, sol. Al: 0.001 to 5% and N: not more than 0.3%, with thebalance being Fe and impurities.

(12) The welded joint structure according to the above (10) or (11), inwhich one or more alloys among the base metals and welding materialcontain one or more elements selected from the first group and thesecond group or both given below in lieu of a part of Fe, by masspercent:

First group: Cu: not more than 5%, Mo: not more than 10%, W: not morethan 10%, V not more than 2%, Nb: not more than 3%, Ti: not more than3%, Ta: not more than 8%, Zr: not more than 1%, Hf: not more than 1%,Co: not more than 15% and B: not more than 0.03%; and

Second group: Ca: not more than 0.05%, Mg: not more than 0.05% and REM:not more than 0.3%.

The term “impurities” so referred to in the phrase “the balance being Feand impurities” indicates those impurities which come from ores, scraps,other raw materials and so on in the industrial production of metallicmaterials.

The term “REM” refers to a total of 17 elements including Sc, Y andlanthanoid collectively, and the REM content mentioned above means thecontent of one element or the total content of two or more elementsamong the REM.

The term “ratio of dilution from base metals” refers to the proportionof the base metals diluted in the weld metal of the primary layerobtained by the combination of the base metals and welding material.

In the following, the above-mentioned inventions (1) to (3) related tothe welding materials and the inventions (4) to (12) related to thewelded joint structures are referred to as “the present invention (1)”to “the present invention (12)”, respectively, or collectively referredto as “the present invention”.

Effects of the Invention

The welding materials of the present invention, in spite of at least oneof the base metals has a high P content of more than 0.03% to not morethan 0.3% and shows fully austenitic solidification, can suppress weldsolidification cracking; therefore, they can be widely used in suchfields where a welding fabrication is required. Furthermore, the weldedjoint structures of the present invention, in spite of at least one ofthe base metals has a high P content mentioned above and shows fullyaustenitic solidification, are excellent in weld solidification crackingresistance or in both weld solidification cracking resistance andductility. In addition, the welded joint structures of the presentinvention also have excellent high temperature strength and corrosionresistance. The welding materials of the present invention are bestsuited for producing the above-mentioned austenitic alloy welded jointstructures.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is the illustration of a tubular material used in the restrainedweld cracking test in the “Example 2”.

BEST MODES FOR CARRYING OUT THE INVENTION

In the following, all of the requirements of the present invention aredescribed in detail. In the following description, the symbol “%” forthe content of each element means “% by mass”.

(A) Chemical compositions of the base metals, welding material and theweld metal in the welded joint structure:

(A-1) Regarding C in the welding material:

(A-1-1) Regarding C in the welding material to be used in the presentinventions (1) and (2):

C: more than 0.3% to not more than 3.0%:

C is one of the most important elements in the welding materialmentioned above. That is to say, C is an indispensable element in orderto promote the crystallization of the Cr-based “M₇C₃” type carbideswhich are necessary for counteracting the malignant influence of anincreased P content on the susceptibility to weld solidificationcracking of austenitic alloys.

When, in welding austenitic alloys having a Cr content of not less than12%, at least one of the base metals contains a high-P amount of morethan 0.03%, that is to say, in the case of similar material welding ofbase metals containing a high concentration of P, or in the case ofdissimilar material welding using base metals only one of which containsa high concentration of P, a C content of more than 0.3% is employed inorder to stably inhibit the susceptibility to solidification crackingfrom increasing as a result of the concentration and inflow of P at aratio of dilution from base metals of about 50%. A higher C content ismore favorable; however, if the content of C is more than 3.0%, anexcessive amount of C flows into the weld metal under certain weldingconditions, often rendering the ductility of the welded joint very poor.Therefore, the content of C is set to more than 0.3% to not less than3.0%. The C content of the above-mentioned welding material ispreferably more than 0.5%, and more preferably not less than 0.8%.

(A-1-2) Regarding C in the welding material for the primary pass of themulti-layer welding which is to be used in the present invention (7):

C: more than 0.6% to not more than 2.0%:

C is one of the most important elements in the welding materialmentioned above. That is to say, C is an indispensable element in orderto promote the crystallization of the Cr-based “M₇C₃” type carbideswhich are necessary for counteracting the malignant influence of anincreased P content on the susceptibility to weld solidificationcracking of austenitic alloys.

When, in welding austenitic alloys having a Cr content of not less than12%, at least one of the base metals contains a high-P amount of morethan 0.03%, that is to say, in the case of the primary pass welding insimilar material welding of base metals containing a high concentrationof P, or in the case of the primary pass welding in dissimilar materialwelding using base metals only one of which contains a highconcentration of P, a C content of more than 0.6% is employed for thewelding material for the primary pass of the multi-layer welding inorder to stably inhibit the susceptibility to solidification crackingfrom increasing as a result of the concentration and inflow of P at aratio of dilution from base metals of not less than 50%, in particular.A higher C content is more favorable for the welding material for theprimary pass of the multi-layer welding; however, if the content of C ismore than 2.0%, coarse eutectic carbides crystallize and/or precipitateout in excessive amounts in the weld metal, rendering the ductility ofthe weld metal of the primary layer very poor. Therefore, the content ofC in the welding material for the primary pass of the multi-layerwelding is set to more than 0.6% to not less than 2.0%. The lower limitof the C in the welding material for the primary pass of the multi-layerwelding mentioned above is preferably 0.8%, and more preferably 1.0%.

(A-1-3) Regarding C in the welding material for the subsequent build-uppasses of the multi-layer welding which is to be used in the presentinvention (7):

C: more than 0.2% to not more than 0.6%:

Even when the ratio of dilution from base metals is not less than 50%,the amounts of P flowing into the weld metal from the primary passwelded portion and base metals in the second and subsequent build-uppasses in the multilayer welding is small. Therefore, the C content ofthe above welding material for the subsequent build-up passes of themulti-layer welding may be relatively low, that is to say, not more than0.6%. If a welding material containing C of more than 0.6% is singlyused for the build-up passes of the multi-layer welding, the weld metalobtained may show reduced ductility. Therefore, in order to provide thewelded joint structures with sufficient ductility, the C content of theabove-mentioned welding material for the subsequent build-up passes ofthe multi-layer welding is set to not more than 0.6%. On the other hand,when the ratio of dilution from base metals is not less than 50% inparticular, the concentration and inflow of P increase. Therefore, forinhibiting the susceptibility to weld solidification cracking in thesubsequent build-up passes of the multi-layer welding from increasing,the C content of the above-mentioned welding material for the subsequentbuild-up passes of the multi-layer welding is set to more than 0.2%. Thelower limit of the C content in the welding material for the subsequentbuild-up passes of the multi-layer welding mentioned above is preferably0.25%, and more preferably 0.3%.

(A-1-4) Regarding C in the welding material to be used in the presentinvention (10):

C: more than 0.2% to not more than 0.6%:

When the ratio of dilution from base metals is less than 50%, at leastin the primary layer, the concentration and inflow of P are small.Therefore, the C content of the welding material to be used in such acase is preferably lower, that is to say, not more than 0.6%; at such aC content level, it becomes possible to prevent the ductility of theresulting weld metal from decreasing and provide the welded jointstructures with sufficient ductility. On the other hand, when the ratioof dilution from base metals is less than 50%, at least in the primarylayer, the susceptibility to solidification cracking resulting fromconcentration and inflow of P can be stably prevented by employing a Ccontent more than 0.2% for the above-mentioned welding material.Therefore, the C content of the above-mentioned welding material is setto more than 0.2% to not more than 0.6%. In cases where the ratio ofdilution from base metals at least in the primary layer is less than50%, the lower limit of the C content in the welding material ispreferably 0.4% in the case of welding where the ratio of dilution frombase metals is not less than 40% in particular; the lower limit of the Ccontent in the welding material is preferably 0.3% in the case ofwelding where the ratio of dilution from base metals is not less than30% in particular.

(A-2) Regarding Cr in the welding material:

(A-2-1) Regarding Cr in the welding material to be used in the presentinventions (1) and (2):

Cr: more than 22% to not more than 55%

Cr is an essential element for forming a thin oxide film on the surfaceof the metallic materials to thereby ensure stainless steels and Nibased alloys oxidation resistance, steam oxidation resistance and hightemperature corrosion resistance and so on. In addition, like C, in theabove-mentioned welding material, Cr is an indispensable element inorder to crystallize the said “M₇C₃” type carbides.

When, in welding austenitic alloys having a Cr content of not less than12%, at least one of the base metals contains a high-P amount of morethan 0.03%, that is to say, in the case of similar material welding ofbase metals containing a high concentration of P, or in the case ofdissimilar material welding using base metals only one of which containsa high concentration of P, the welding material is required to have a Crcontent of more than 22% so as to stably inhibit the susceptibility tosolidification cracking from increasing as a result of the concentrationand inflow of P at a ratio of dilution from base metals of about 50%.However, if the content of Cr is more than 55%, it becomes verydifficult, in view of the balance with the Ni content, to ensure thestability of a fully austenitic microstructure which is necessary forsecuring creep strength for a long period of time and, in addition,coarse carbides precipitate out in large amounts; thus markeddeterioration of mechanical properties, for example age-toughness and soon, sometimes occur. Therefore, the content of Cr is set to more than22% to not more than 55%. The Cr content of the above-mentioned weldingmaterial is more preferably less than 40%.

(A-2-2) Regarding Cr in the welding material for the primary pass andthe subsequent build-up passes of the multi-layer welding which are tobe used in the present invention (7), and in the welding material to beused in the present invention (10):

Cr: more than 22% to not more than 35%

As mentioned above, Cr is an essential element for forming a thin oxidefilm on the surface of the metallic materials to thereby ensurestainless steels and Ni based alloys oxidation resistance, steamoxidation resistance and high temperature corrosion resistance and soon. In addition, like C, in the above-mentioned welding materials aswell, Cr is an indispensable element in order to crystallize the said“M₇C₃” type carbides.

When, in welding austenitic alloys having a Cr content of not less than12%, at least one of the base metals contains a high-P amount of morethan 0.03%, that is to say, in the case of similar material welding ofbase metals containing a high concentration of P or in the case ofdissimilar material welding using base metals only one of which containsa high concentration of P, the welding material is required to have a Crcontent of more than 22% so as to stably inhibit the susceptibility tosolidification cracking from increasing as a result of the concentrationand inflow of P at a ratio of dilution from base metals of not less than50%. Similarly, also when the ratio of dilution from base metals atleast in the primary layer is less than 50%, the welding material isrequired to have a Cr content of more than 22% so as to stably inhibitthe susceptibility to solidification cracking from increasing as aresult of the concentration and inflow of P.

However, in both the case where the ratio of dilution from base metalsis not less than 50% and the case where the ratio of dilution from basemetals at least in the primary layer is less than 50%, a Cr content ofmore than 35% may deteriorate the ductility of the weld metal as aresult of crystallizing of coarse eutectic carbides in excessiveamounts. Therefore, the content of Cr in the welding materials mentionedabove is set to more than 22% to not more than 35%. The Cr content ofthe welding materials mentioned above is more preferably not more than33%.

(A-3) Regarding elements other than C and Cr in the welding material:

(A-3-1) Regarding elements other than C and Cr in the welding materialto be used in the present inventions (1), (7) and (10):

Si: not more than 4.0%

Si is an element which reacts with O (oxygen) coming from the air on theoccasion of welding to thereby produce a deoxidizing effect and furtheris effective in increasing oxidation resistance, steam oxidationresistance and so on of the resulting weld metal. In order to obtain theabove-mentioned effects, it is preferable to contain a Si content of notless than 0.1%. However, when the content of Si becomes excessive, inparticular when it exceeds 4.0%, the susceptibility to weldsolidification cracking markedly increases. Therefore, the content of Siis set to not more than 4.0%. The content of Si is more preferably notmore than 3.0% and further more preferably not more than 2.0%.

Mn; not more than 3.0%

Mn is an element effective in preventing hot working brittleness due tothe S which is contained as an impurity in the metallic materials and,in addition, Mn is effective in deoxidation on the occasion of meltingthe materials. In order to obtain these effects, a Mn content of notless than 0.01% is preferable. However, if the content of Mn exceeds3.0%, it promotes the precipitation of such intermetallic compounds asthe σ phase and so on; thus a decrease in toughness and/or ductility dueto the deterioration of microstructural stability at high temperaturesoccurs. Therefore, the content of Mn is set to not more than 3.0%. Thecontent of Mn is more preferably 0.10 to 2.0% and further morepreferably 0.30 to 1.5%.

P; not more than 0.03%

P is conventionally known to be an element which markedly increases thesusceptibility to weld solidification cracking. In the case of the fullyaustenitic solidification, in particular, the said malignant influencemarkedly increases. In the present invention, although the P content ofthe austenitic alloy which constructs at least one of the base metals isincreased in order to ensure high temperature strength and corrosionresistance, the P content of the welding material is set to not morethan 0.03% in order to reduce the susceptibility to weld solidificationcracking and also in order to suppress the P content in the weld metal.The content of P is more preferably not more than 0.02%, and furthermore preferably not more than 0.01%.

S: not more than 0.03%

S is an impurity element coming from raw materials, for example, in thestep of melting the metallic materials. A high content of S causes thedeterioration of corrosion resistance and it also deteriorates the hotworkability and weldability; in particular, when the content of Sexceeds 0.03%, the corrosion resistance, hot workability and weldabilitymarkedly deteriorate. Therefore, the content of S is set to not morethan 0.03%. It is desirable that the S content be reduced as low aspossible; therefore, the content of S is preferably not more than 0.01%and more preferably not more than 0.005%.

Ni: more than 30% to not more than 70%

Ni is an essential element for ensuring a stable austeniticmicrostructure. As mentioned hereinabove, it is necessary, for thewelding material according to the present invention, that the content ofCr be more than 22%. If the Ni content is not more than 30% relative tothe above-mentioned Cr content, it is difficult for the obtained weldmetal to have a stable single phase of austenitic microstructure and, atthe same time, the austenitic microstructure becomes unstable during along period of use at high temperatures. Also the high temperaturestrength and toughness are markedly deteriorated due to precipitation ofsuch brittle phases as the σ phase and so on. On the other hand, as theNi content increases, the amount of P which is dissolved in austenitedecreases and the malignant influence of P on the susceptibility to weldsolidification cracking increases. In particular, when the content of Niexceeds 70%, the solubility of P in the matrix is reduced and,accordingly, the concentration of P in the liquid phase becomes moreenhanced and, as a result, the susceptibility to weld solidificationcracking becomes very high; moreover, the component cost also piles up.Therefore, the content of Ni is set to more than 30% to not more than70%. The content of Ni is more preferably 35 to 65%.

Sol. Al: 0.001 to 1%

Al reacts with O (oxygen) coming from the air on the occasion of weldingto thereby produces a deoxidizing effect. In order to obtain thiseffect, it is necessary that the content of Al as sol. Al (“acid-solubleAl”) be not less than 0.001%. However, when the content of Al as sol. Alexceeds 1%, excessive amounts of intermetallic compounds precipitate athigh temperatures; thus the toughness markedly decreases. In the abovecase, the marked decrease in ductility may also occur. Therefore, thecontent of sol. Al is set to 0.001 to 1%.

N: not more than 0.3%

When the content of N exceeds 0.3%, it causes a deterioration of hotworkability. Therefore, the content of N is set to not more than 0.3%.It is desirable that the N content be as low as possible; therefore, thecontent of N is more preferably not more than 0.2% and further morepreferably not more than 0.15%.

From the reasons mentioned above, the basic chemical compositions of thewelding materials, according to the present inventions (1) to (4), aredefined as the ones which comprise C: more than 0.3% to not more than3.0%, Si: not more than 4.0%, Mn: not more than 3.0%, P: not more than0.03%, S: not more than 0.03%, Cr: more than 22% to not more than 55%,Ni: more than 30% to not more than 70%, sol. Al: 0.001 to 1% and N: notmore than 0.3%, with the balance being Fe and impurities.

Moreover, the basic chemical compositions of the welding materials forthe primary pass of the multi-layer welding which is to be used forobtaining the welded joint structures, according to the presentinventions (7) to (9), are defined as the ones which comprise C: morethan 0.6% to not more than 2.0%, Si: not more than 4.0%, Mn: not morethan 3.0%, P: not more than 0.03%, S: not more than 0.03%, Cr: more than22% to not more than 35%, Ni: more than 30% to not more than 70%, sol.Al: 0.001 to 1% and N: not more than 0.3%, with the balance being Fe andimpurities.

Further, both the basic chemical compositions, of the welding materialsfor the subsequent build-up passes of the multi-layer welding which isto be used for obtaining the welded joint structures according to thepresent inventions (7) to (9) and, of the welding materials to be usedfor obtaining the welded joint structures according to the presentinventions (10) to (12), are defined as the ones which comprise C: morethan 0.2% to not more than 0.6%, Si: not more than 4.0%, Mn: not morethan 3.0%, P: not more than 0.03%, S: not more than 0.03%, Cr: more than22% to not more than 35%, Ni: more than 30% to not more than 70%, sol.Al: 0.001 to 1% and N: not more than 0.3%, with the balance being Fe andimpurities.

And furthermore, the basic chemical compositions of the weldingmaterials to be used for obtaining the welded joint structures,according to the present inventions (10) to (12), are defined as theones which comprise C: more than 0.2% to not more than 0.6%, Si: notmore than 4.0%, Mn: not more than 3.0%, P: not more than 0.03%, S: notmore than 0.03%, Cr: more than 22% to not more than 35%, Ni: more than30% to not more than 70%, sol. Al: 0.001 to 1% and N: not more than0.3%, with the balance being Fe and impurities.

The welding material to be used for the primary pass welding may be inthe form of a solid wire or a spool; insert rings may also be used.

(A-4) Regarding base metals to be used in the present inventions (1),(2), (5), (7), (8), (10) and (11):

C: not more than 2.0%

C is an element which enhances the high temperature strength. In orderto obtain this effect, it is preferable to contain a C content of notless than 0.01%. On the other hand, when the C content is excessive, inparticular when it exceeds 2.0%, excessive amounts of Cr carbidescrystallize out or precipitate; therefore, marked deterioration inductility of materials occurs. Furthermore, the temperature which ishigh and at which the ductility is lost (the so-called “zero ductilitytemperature”) has fallen markedly or marked deteriorations in ductilityare caused in the vicinity of about 1000° C., accordingly, the hotworkability is markedly deteriorated. Therefore, the content of C is setto not more than 2.0%.

Si: not more than 4.0%

Si is an element having a deoxidizing effect in the step of melting themetallic materials and further is effective in increasing the oxidationresistance, steam oxidation resistance and so on. In order to obtain theeffects mentioned above, it is preferable to contain a Si content of notless than 0.1%. However, when the content of Si becomes excessive, inparticular when it exceeds 4.0%, the susceptibility to weldsolidification cracking markedly increases. Therefore, the content of Siis set to not more than 4.0%. The content of Si is more preferably notmore than 3.0% and further more preferably not more than 2.0%.

Mn: 0.01 to 3.0%

Mn is an element effective in preventing hot working brittleness due tothe S which is contained as an impurity in the metallic materials and,in addition, Mn is effective in deoxidation on the occasion of meltingthe materials. In order to obtain these effects, a content of Mn notless than 0.01% is necessary. However, if the content of Mn exceeds3.0%, it promotes the precipitation of such intermetallic compounds asthe σ phase and so on; thus a decrease in toughness and/or ductility dueto the deterioration of microstructural stability at high temperaturesoccurs. Therefore, the content of Mn is set to 0.01 to 3.0%. The contentof Mn is more preferably 0.10 to 2.0% and further more preferably 0.30to 1.5%.

P: more than 0.03% to not more than 0.3% (in the “chemical composition1” mentioned above and in the base metals to be used in the presentinvention (5))

P is conventionally known to be an element which markedly increases thesusceptibility to weld solidification cracking. In the case of the fullyaustenitic solidification, in particular, the said malignant influenceincreases markedly. Therefore, the content thereof has been restricted.However, a P content of more than 0.03% is effective in improvingmaterial characteristics, for example in bringing about improvements inhigh temperature strength, corrosion resistance and so on. On the otherhand, an excessively high P content, in particular a P content of morethan 0.3% deteriorates the very performance characteristics of the basemetals. Therefore, both of the P contents, in the above-mentioned“chemical composition 1” being included in the base metals of thepresent inventions (1), (2), (7), (8), (10) and (11) and in the basemetals to be used in the present invention (5), are set to more than0.03% to not more than 0.3%. Both of the P contents, in the “chemicalcomposition 1” and in the base metals to be used in the presentinvention (5), are more preferably over 0.05% to not more than 0.3% andfurther more preferably over 0.08% to not more than 0.2%.

P: not more than 0.03% (in the “chemical composition 2” mentioned above)

In the present inventions (2), (8) and (11), the base metal having the“chemical composition 2” is a base metal to be submitted to “dissimilarmaterial welding” to a base metal having a P content more than 0.03% tonot more than 0.3% as shown in the “chemical composition 1” mentionedabove. As already mentioned hereinabove, P is conventionally known to bean element which markedly increases the susceptibility to weldsolidification cracking, and in the case of the fully austeniticsolidification, in particular, the said malignant influence increasesmarkedly. Therefore, for the purpose of reducing the susceptibility toweld solidification cracking, the P content in the above-mentioned“chemical composition 2” being included in the base metals to be used inthe present inventions (2), (8) and

(11) is set to not more than 0.03%. The P content in the “chemicalcomposition 2” is more preferably not more than 0.02%.

S: not more than 0.03%

S is an impurity element coming from raw materials, for example, in thestep of melting the metallic materials. A high content of S causes thedeterioration of corrosion resistance and it also deteriorates the hotworkability and weldability; in particular, when the content of Sexceeds 0.03%, the corrosion resistance, hot workability and weldabilitymarkedly deteriorate. Therefore, the content of S is set to not morethan 0.03%. It is desirable that the S content be reduced as low aspossible; therefore, the content of S is preferably not more than 0.01%and more preferably not more than 0.005%.

Cr: 12 to 35%

Cr is an essential element for forming a thin oxide film on the surfaceof the metallic materials to thereby ensure stainless steels and Nibased alloys oxidation resistance, steam oxidation resistance and hightemperature corrosion resistance and so on. In order to obtain theabove-mentioned effects, it is necessary to include a Cr content of notless than 12%.

In the present invention, in order to counteract the malignant influenceof P on the susceptibility to weld solidification cracking, it isnecessary to crystallize the said Cr-based “M₇C₃” type carbides.Moreover, a higher Cr content brings about a greater improvement incorrosion resistance. Therefore, a higher Cr content is desired.However, if the content of Cr is more than 35%, it becomes verydifficult, in view of the balance with the Ni content, to ensure thestability of a fully austenitic microstructure which is necessary forsecuring creep strength for a long period of time and, in addition,coarse carbides precipitate out in large amounts; thus markeddeterioration of mechanical properties, for example age-toughness and soon, occur. Therefore, the content of Cr is set to 12 to 35%.

Ni: 6 to 80%

Ni is an essential element for ensuring a stable austeniticmicrostructure and the necessary minimum content thereof is determinedby the contents of elements contained in the austenitic alloys such asCr, Mo, W, Nb and the like, which are the ferrite-forming elements, andMn, C, N and so on, which are the austenite-forming elements.

As mentioned hereinabove, it is necessary, for the base metals accordingto the present invention, that the content of Cr be not less than 12%.If the Ni content is less than 6% relative to the above-mentioned Crcontent, it is difficult to form a stable single phase of austeniticmicrostructure and, further the austenitic microstructure becomesunstable during a long period of use at high temperatures and the hightemperature strength and toughness are markedly deteriorated due toprecipitation of such brittle phases as the σ phase and so on. On theother hand, as the Ni content increases, the amount of P which isdissolved in austenite decreases and the malignant influence of P on thesusceptibility to weld solidification cracking increases. In particular,when the content of Ni exceeds 80%, the solubility of P in the matrix isreduced and, accordingly, the concentration of P in the liquid phasebecomes more enhanced and, as a result, the susceptibility to weldsolidification cracking becomes very high; moreover, the component costalso piles up. Therefore, the content of Ni is set to 6 to 80%. Thecontent of Ni is more preferably 8 to 55%.

Sol. Al: 0.001 to 5%

Al has deoxidizing effect in the step of melting the metallic materials.In order to obtain this effect, it is necessary that the content of Alas sol. Al (“acid-soluble Al”) be not less than 0.001%. When Al iscontained at a high concentration, it forms the y′ phase, which isstable at high temperatures; and thus Al contributes toward improvementsin creep strength and also contributes toward improvements in corrosionresistance at high temperatures through oxide film formation. However,when the content of Al as sol. Al exceeds 5%, excessive amounts ofintermetallic compounds precipitate at high temperatures; thus thetoughness markedly decreases. In the above case, a marked decrease ofductility may also occur. Therefore, the content of sol. Al is set to0.001 to 5%. The content of sol.Al is more preferably 0.005 to 3% andfurther more preferably 0.01 to 1%.

N: not more than 0.3%

When the content of N exceeds 0.3%, it causes a deterioration of hotworkability. Therefore, the content of N is set to not more than 0.3%.It is desirable that the N content be as low as possible; therefore, thecontent of N is more preferably not more than 0.2% and further morepreferably not more than 0.15%.

From the reasons mentioned above, the “chemical composition 1” beingincluded in the base metals of the present inventions (1), (2), (7),(8), (10) and (11) is defined as the one which comprise C: not more than2.0%, Si: not more than 4.0%, Mn: 0.01 to 3.0%, P: more than 0.03% tonot more than 0.3%, S: not more than 0.03%, Cr: 12 to 35%, Ni: 6 to 80%,sol. Al: 0.001 to 5% and N: not more than 0.3%, with the balance beingFe and impurities.

From the same reasons, the chemical composition of the base metal to beused in the present invention (5) is defined as the one which comprisesC: not more than 2.0%, Si: not more than 4.0%, Mn: 0.01 to 3.0%, P: morethan 0.03% to not more than 0.3%, S: not more than 0.03%, Cr: 12 to 35%,Ni: 6 to 80%, sol. Al: 0.001 to 5% and N: not more than 0.3%, with thebalance being Fe and impurities.

Further, the “chemical composition 2” being included in the base metalsof the present inventions (2), (8) and (11) is defined as the one whichcomprises C: not more than 2.0%, Si: not more than 4.0%, Mn: 0.01 to3.0%, P: not more than 0.03%, S: not more than 0.03%, Cr: 12 to 35%, Ni:6 to 80%, sol. Al: 0.001 to 5% and N: not more than 0.3%, with thebalance being Fe and impurities.

(A-5) Regarding weld metal in the welded joint structure to be used inthe present invention (5):

In the weld metal in a welded joint structure according to the presentinvention (5), the chemical composition of at least the primary layerbeing welded from one side must comprise C: more than 0.1% to not morethan 0.7%, Si: not more than 4.0%, Mn: not more than 3.0%, P: more than0.03% to not more than 0.1%, S: not more than 0.03%, Cr: 18 to 30%, Ni:more than 10% to not more than 70%, sol. Al: 0.001 to 1% and N: not morethan 0.3%, with the balance being Fe and impurities. In the following,these requirements are explained.

C: more than 0.1% to not more than 0.7%

C is one of the most important elements in the present invention. Thatis to say, C is an indispensable element in order to promote thecrystallization of the Cr-based “M₇C₃” type carbides which are necessaryfor counteracting the malignant influence of an increased P content onthe susceptibility to weld solidification cracking of austenitic alloys.

In welding austenitic alloys having a Cr content of not less than 12%,in order to stably inhibit solidification cracking even when P comesfrom base metals which contains P at a high level of more than 0.03%, itis necessary that at least the primary layer being welded from one sideof the weld metal (hereinafter also referred to as “primary layer of theweld metal in one side welding”) contain C content of more than 0.1%. Ahigher C content is more favorable; however, if the content of C is morethan 0.7%, the ductility of the weld metal may sometimes become verypoor. Therefore, the content of C in the primary layer of the weld metalin one side welding is set to more than 0.1% to not more than 0.7%. Theabove-mentioned C content is more preferably more than 0.2% and furthermore preferably more than 0.3%.

Si: not more than 4.0%

Si is an element having a deoxidizing effect on the occasion of weldingand further is effective in increasing the oxidation resistance, steamoxidation resistance and so on. In order to obtain the effects mentionedabove, it is preferable to contain a Si content of not less than 0.1% inthe primary layer of the weld metal in one side welding. However, whenthe content of Si becomes excessive, in particular when it exceeds 4.0%,the susceptibility to weld solidification cracking markedly increases.Therefore, the content of Si is set to not more than 4.0%. The contentof Si is more preferably not more than 3.0% and further more preferablynot more than 2.0%.

Mn: not more than 3.0%

Mn is an element effective in preventing hot working brittleness due tothe S which is contained as an impurity in the metallic materials and,in addition, Mn is effective in deoxidation on the occasion of welding.In order to obtain these effects, it is preferable to contain a Mncontent of not less than 0.01% in the primary layer of the weld metal inone side welding. However, if the content of Mn exceeds 3.0%, itpromotes the precipitation of such intermetallic compounds as the σphase and so on; thus a decrease in toughness and/or ductility due tothe deterioration of microstructural stability at high temperaturesoccurs. Therefore, the content of Mn is set to not more than 3.0%. Thecontent of Mn is more preferably 0.10 to 2.0% and further morepreferably 0.30 to 1.5%.

P: more than 0.03% to not more than 0.1%

P is conventionally known to be an element which markedly increases thesusceptibility to weld solidification cracking. In the case of the fullyaustenitic solidification, in particular, the said malignant influenceincreases markedly. In the present invention (5), however, base metalshaving an increased P content are used for bringing about improvementsin high temperature strength and corrosion resistance and, therefore,from the viewpoint of ensuring high temperature strength and corrosionresistance, the content of P in the primary layer of the weld metal inone side welding is set to more than 0.03%. However, an excessively highP content, in particular a P content of more than 0.1% increases thesusceptibility to weld solidification cracking. Therefore, the contentof P is set to more than 0.03% to not more than 0.1%. From the viewpointof high temperature strength, the content of P is more preferably morethan 0.04% and further more preferably more than 0.05%.

S: not more than 0.03%

A high content of S causes the deterioration of corrosion resistance andit also deteriorates the weldability; in particular, when the content ofS exceeds 0.03%, the corrosion resistance and weldability markedlydeteriorate. Therefore, the content of S in the primary layer of theweld metal in one side welding is set to not more than 0.03%. It isdesirable that the S content be reduced as low as possible; therefore,the content of S is preferably not more than 0.01% and more preferablynot more than 0.005%.

Cr: 18 to 30%

Cr is an essential element for forming a thin oxide film on the surfaceof the metallic materials to thereby ensure stainless steels and Nibased alloys oxidation resistance, steam oxidation resistance and hightemperature corrosion resistance and so on. In addition, like C, in thepresent invention Cr is an indispensable element in order to crystallizethe said “M₇C₃” type carbides. In order to stably inhibit solidificationcracking even when P comes from base metals which contains P at a highlevel of more than 0.03%, it is necessary for the primary layer of theweld metal in one side welding to contain a Cr content of not less than18%. However, when the content of Cr exceeds 30%, it becomes difficultto ensure the ductility of the welded joint. Therefore, the content ofCr is set to 18 to 30%.

Ni: more than 10% to not more than 70%

Ni is an essential element for ensuring a stable austeniticmicrostructure. As mentioned above, in the present invention (5), it isnecessary for the primary layer of the weld metal in one side welding tocontain a Cr content of not less than 18%. If the Ni content is not morethan 10% relative to the above-mentioned Cr content, it is difficult forthe weld metal obtained in one side welding to form a stable singlephase of austenitic microstructure and, furthermore, the austeniticmicrostructure becomes unstable during a long period of use at hightemperatures and the high temperature strength and toughness aremarkedly deteriorated due to precipitation of such brittle phases as theσ phase and so on. On the other hand, as the Ni content increases, theamount of P which is dissolved in austenite decreases and the malignantinfluence of P on the susceptibility to weld solidification crackingincreases. In particular, when the content of Ni exceeds 70%, thesusceptibility to weld solidification cracking becomes very high;moreover, the component cost also piles up. Therefore, the content of Niis set to more than 10% to not more than 70%. The content of Ni is morepreferably 25 to 50%.

Sol. Al: 0.001 to 1%

Al reacts with O (oxygen) coming from the air on the occasion of weldingto thereby produces a deoxidizing effect. In order to obtain thiseffect, it is necessary that the content of Al as sol. Al (“acid-solubleAl”) be not less than 0.001%. However, when the content of Al as sol. Alexceeds 1%, excessive amounts of intermetallic compounds precipitate athigh temperatures; thus the toughness markedly decreases. Therefore, thecontent of sol. Al is set to 0.001 to 1%.

N: not more than 0.3%

When the content of N exceeds 0.3%, it causes precipitation of nitridessuch as Cr₂N and so on; and thus causes a deterioration of suchmechanical properties as bendability and toughness of the weld metal.Therefore, the content of N is set to not more than 0.3%. It isdesirable that the N content be reduced as low as possible; therefore,the content of N is preferably not more than 0.2% and more preferablynot more than 0.15%.

From the reasons mentioned above, the chemical composition of at leastthe primary layer being welded from one side of the weld metal in thewelded joint structure according to the present invention (5) is definedas the one which comprises C: more than 0.1% to not more than 0.7%, Si:not more than 4.0%, Mn: not more than 3.0%, P: more than 0.03% to notmore than 0.1%, S: not more than 0.03%, Cr: 18 to 30%, Ni: more than 10%to not more than 70%, sol. Al: 0.001 to 1% and N: not more than 0.3%,with the balance being Fe and impurities.

(A-6) Regarding base metals and welding material according to thepresent inventions (3); base metals and weld metal according to thepresent invention (6); base metals and welding material according to thepresent inventions (9); and base metals and welding material accordingto the present inventions (12):

At least one material among the base metals and welding material of thepresent inventions (1) or (2); at least one of the base metals and weldmetal of the present invention (5); at least one material among the basemetals and welding material of the present invention (7) or (8); and atleast one of the base metals and welding material of the presentinvention (10) or (11), may further contain, in lieu of a part of Fe,according to need, one or more elements selected from the first groupand/or second group listed below.

First group: Cu: not more than 5%, Mo: not more than 10%, W: not morethan 10%, V: not more than 2%, Nb: not more than 3%, Ti: not more than3%, Ta: not more than 8%, Zr: not more than 1%, Hf: not more than 1%,Co: not more than 15% and B: not more than 0.03%.

Second group: Ca: not more than 0.05%, Mg: not more than 0.05% and REM:not more than 0.3%.

That is to say, one or more of the first group and/or the second groupof elements mentioned above may be contained as an optional element orelements.

The above-mentioned optional elements will be explained below.

Each of Cu, Mo, W, V, Nb, Ti, Ta, Zr, Hf, Co and B being elements of thefirst group, if added, has the effect of enhancing the creep strength.In order to obtain this effect, the said elements may be added to thealloys and thereby contained therein. In the following, the elements,which are in the first group, are described in detail.

Cu: not more than 5%

Cu precipitates as the state of the fine Cu phase coherently with theaustenitic matrix during the use at high temperatures. Thus Cu has theeffect of markedly enhancing the creep strength. Cu is also effective ininhibiting CO from dissociating to thereby prevent C from entering thesteel and thus brings about marked improvements in corrosion resistance.In order to ensure the above-mentioned effects, the content of Cu ispreferably not less than 0.01%. However, when the content of Cu becomesexcessive, in particular, when it exceeds 5%, deterioration of hotworkability, weldability and creep ductility occurs. Therefore, when Cuis included, the content of Cu is set to not more than 5%. If Cu isincluded, the content of Cu is preferably 0.01 to 5%. The upper limit ofthe Cu content is more preferably 4.0% and further more preferably 3.0%.

Mo: not more than 10%

Mo is an effective element which improves the high temperature strengthssuch as creep strength and so on. In order to ensure the above-mentionedeffects, the content of Mo is preferably not less than 0.05%. However,when Mo is included at a content level exceeding 10%, the said effect issaturated and alloying cost increases. In addition, the formation ofintermetallic compounds such as the σ phase and so on is induced; hencedeterioration of microstructural stability and hot workability occurs.Therefore, when Mo is included, the content of Mo is set to not morethan 10%. If Mo is included, the content of Mo is preferably 0.05 to 10%and more preferably 0.05 to 5%.

W: not more than 10%

W is also an effective element which improves the high temperaturestrengths such as creep strength and so on. In order to ensure the saideffects, the content of W is preferably not less than 0.05%. However,when W is included at a content level exceeding 10%, the said effect issaturated and alloying cost increases. In addition, the formation ofintermetallic compounds such as the σ phase and so on is induced; hencedeterioration of microstructural stability and hot workability occurs.Therefore, when W is included, the content of W is set to not more than10%. If W is included, the content of W is preferably 0.05 to 10% andmore preferably 0.05 to 5%.

V: not more than 2%

V is a carbide-forming element and is an effective element whichimproves the high temperature strengths such as creep strength and soon. In order to ensure the above-mentioned effects, the content of V ispreferably not less than 0.02%. However, if the content of V exceeds 2%,marked deterioration of mechanical properties such as toughness and soon occurs. Therefore, when V is included, the content of V is set to notmore than 2%. If V is included, the content of V is preferably 0.02 to2% and more preferably 0.02 to 1.5%. Further more preferably, thecontent of V is 0.04 to 1%.

Nb: not more than 3%

Nb is a carbide-forming element and is an effective element whichimproves the high temperature strengths such as creep strength and soon. In order to ensure the said effects, the content of Nb is preferablynot less than 0.05%. However, if the content of Nb exceeds 3%, markeddeterioration of mechanical properties such as toughness and so onoccurs. Therefore, when Nb is included, the content of Nb is set to notmore than 3%. If Nb is included, the content of Nb is preferably 0.05 to3% and more preferably 0.05 to 1.5%.

Ti: not more than 3%

Ti is a carbide-forming element and is an effective element whichimproves the high temperature strengths such as creep strength and soon. In order to ensure the above-mentioned effects, the content of Ti ispreferably not less than 0.005%. However, if the content of Ti exceeds3%, marked deterioration of mechanical properties such as toughness andso on occurs. Therefore, when Ti is included, the content of Ti is setto not more than 3%. If Ti is included, the content of Ti is preferably0.005 to 3% and more preferably 0.005 to 2%.

Ta: not more than 8%

Ta is also a carbide-forming element and is an effective element whichimproves the high temperature strengths such as creep strength and soon. In order to ensure the said effects, the content of Ta is preferablynot less than 0.01%. However, if the content of Ta exceeds 8%, markeddeterioration of mechanical properties such as toughness and so onoccurs. Therefore, when Ta is included, the content of Ta is set to notmore than 8%. If Ta is included, the content of Ta is preferably 0.01 to8% and more preferably 0.01 to 7%. Further more preferably, the contentof Ta is 0.05 to 6%.

Zr: not more than 1%

Zr mainly contributes to grain boundary strengthening and brings aboutimprovements in creep strength. In order to ensure the said effects, thecontent of Zr is preferably not less than 0.0005%. However, if thecontent of Zr exceeds 1%, deterioration of mechanical properties andweldability occurs. Therefore, when Zr is comprised, the content of Zris set to not more than 1%. If Zr is comprised, the content of Zr ispreferably 0.0005 to 1% and more preferably 0.01 to 0.8%. Further morepreferably, the content of Zr is 0.02 to 0.5%.

Hf: not more than 1%

Hf also mainly contributes to grain boundary strengthening and bringsabout improvements in creep strength. In order to ensure theabove-mentioned effects, the content of Hf is preferably not less than0.0005%. However, if the content of Hf exceeds 1%, deterioration ofmechanical properties and weldability occurs. Therefore, when Hf isincluded, the content of Hf is set to not more than 1%. If Zr isincluded, the content of Hf is preferably 0.0005 to 1% and morepreferably 0.01 to 0.8%. Further more preferably, the content of Hf is0.02 to 0.5%.

Co: not more than 15%

Like Ni, Co stabilizes the austenitic microstructure and has the effectof enhancing the creep strength. In order to ensure the said effects,the content of Co is preferably not less than 0.05%. However, at a Cocontent level which exceeds 15%, the said effects of Co arrive atsaturation levels and the economic efficiency only declines. Therefore,when Co is included, the content of Co is set to not more than 15%. IfCo is included, the content of Co is preferably 0.05 to 10%.

B: not more than 0.03%

B exists in carbonitrides and promotes finely dispersed precipitation ofcarbonitrides during the use at high temperatures, and at the same time,B exists singly at grain boundaries and therefore strengthens grainboundaries and prevents grain boundary sliding. And thereby, B enhancesthe creep strength. In order to ensure the said effects, the content ofB is preferably set to not less than 0.0005%. However, if the content ofB exceeds 0.03%, deterioration of weldability occurs. Therefore, when Bis comprised, the content of B is set to not more than 0.03%. If B iscomprised, the content of B is preferably 0.0005 to 0.03% and morepreferably 0.001 to 0.01%. Further more preferably, the content of B is0.001 to 0.005%.

The above-mentioned elements, namely Cu, Mo, W, V, Nb, Ti, Ta, Zr, Hf,Co and B may be included singly, or two or more of them may be includedin combination.

Each of Ca, Mg and REM being elements of the second group, if added, hasthe effect of improving the hot workability. In order to obtain thiseffect, the said elements may be added to the alloys and therebycontained therein. In the following, the elements, which are in thesecond group, are described in detail.

Ca: not more than 0.05%

Ca has an effect of improving the hot workability. In order to ensurethis effect, the content of Ca is preferably set to not less than0.0001%. However, a Ca content which exceeds 0.05% causes a decrease inhot workability due to the formation of oxide type inclusions and alsocauses deterioration of ductility. Therefore, when Ca is included, thecontent of Ca is set to not more than 0.05%. If Ca is included, thecontent of Ca is preferably 0.0001 to 0.05% and more preferably 0.001 to0.02%. Further more preferably, the content of Ca is 0.001 to 0.01%.

Mg: not more than 0.05%

Mg also has an effect of improving the hot workability. In order toensure this effect, the content of Mg is preferably set to not less than0.0005%. However, a Mg content which exceeds 0.05% causes a decrease inhot workability due to the formation of oxide type inclusions and alsocauses deterioration of ductility. Therefore, when Mg is included, thecontent of Mg is set to not more than 0.05%. If Mg is included, thecontent of Mg is preferably 0.0005 to 0.05% and more preferably 0.001 to0.02%. Further more preferably, the content of Mg is 0.001 to 0.01%.

REM: not more than 0.3%

REM has an affinity for impurity elements which are contained inmetallic materials; in particular REM has a high affinity for S and,therefore, has an effect for preventing deterioration of hot workabilitydue to the S being excessively contained. This effect becomes markedlywhen the content of REM is not less than 0.005%. However, a REM contentwhich exceeds 0.3% induces the formation of coarse oxides and sulfides;and thus causes deterioration of hot workability and, further, causes anincreased number of surface defects as well as deterioration oftoughness. Therefore, when REM is included, the content of REM is set tonot more than 0.3%. If REM is included, the content of REM is preferably0.005 to 0.3% and more preferably 0.005 to 0.1%. Further morepreferably, the content of REM is 0.005 to 0.07%.

The above-mentioned elements, namely Ca, Mg and REM may be includedsingly, or two or more of them may be included in combination.

As already mentioned hereinabove, the term “REM” refers to a total of 17elements including Sc, Y and lanthanoid collectively, and the REMcontent means the content of one or the total content of two or more ofthe REM.

From the reasons mentioned above, in the present invention (3), it hasbeen stipulated that one or more alloys among the base metals andwelding material further contain, respectively and according to need,one or more elements selected from the first group and the second groupor both mentioned above in addition to the elements according to thepresent invention (1) or (2). It has also been stipulated that, in thepresent invention (9), one or more alloys among the base metals andwelding material further contain, respectively and according to need,one or more elements selected from the first group and the second groupor both mentioned above in addition to the elements according to thepresent invention (7) or (8). Similarly, it has been stipulated that, inthe present invention (12); one or more alloys among the base metals andwelding material further contain, respectively and according to need,one or more elements selected from the first group and the second groupor both mentioned above in addition to the elements according to thepresent invention (10) or (11).

From the same reasons, in the present invention (6), it has beenstipulated that one or both of the base metals further contain one ormore elements selected from the first group and the second group or bothmentioned above in addition to the base metal elements according to thepresent invention (5).

Further, in the present invention (6), it has been stipulated that aweld metal further contains one or more elements selected from the firstgroup and the second group or both mentioned above in addition to theweld metal elements according to the present invention (5).

The welding materials according to the present inventions (1) to (3) andthe welding materials to be used on the occasion of producing the weldedjoint structures according to the present inventions (7) to (12) can beproduced, for example, by melting alloys having the respectivecompositions mentioned above, followed by working into wires by forgingand rolling. The welding materials according to the present inventions(1) to (3) and the welding materials to be used on the occasion ofprimary pass welding in producing the welded joint structures accordingto the present inventions (7) to (9) can also be produced in the form ofinsert rings and further can be produced by covering or coating Cr—Nialloy plate sheath materials with a high-C—Cr—Ni alloy powder, ahigh-C—Cr alloy powder and so on, followed by wire drawing so as toattain the respective regulated chemical compositions.

The welding materials according to the present inventions (1) to (3) canbe used in various welding processes such as TIG welding and MIG weldingand so on.

Therefore, the welded joint structure of the present invention (4) canbe produced by welding together the austenitic alloy base metalsaccording to any one of the present inventions (1) to (3) by variouswelding methods using the welding material according to any one of thepresent inventions (1) to (3).

In cases where multi-layer welding is required in welding together thebase metals according to any one of the present inventions (1) to (3) togive the welded joint structure according to the present invention (4),the multi-layer welding may also be carried out using the weldingmaterial according to any one of the present inventions (1) to (3).

In cases where high levels of corrosion resistance and creep strengthare required in the weld metal, it is also possible to carry out theprimary pass welding, in which the ratio of dilution from base metals ishigh, using the welding material according to any one of the presentinventions (1) to (3) and, in the subsequent build-up passes, carry outthe welding using a commercially available welding material properlyselected according to the ratio of dilution from base metals, whichinfluences the weld solidification cracking. For example, in the case ofwelding where the ratio of dilution from base metals is fairly low suchas not more than 20%, it may use a commercially available weldingmaterial according to the required levels of corrosion resistance andcreep strength.

Like the welding materials according to the present inventions (1) to(3), the welding materials to be used on the occasion of producing thewelded joint structures according to the present inventions (7) to (12)can be used in various welding processes such as TIG welding and MIGwelding and so on.

Therefore, the welded joint structures of the present inventions (7) to(9) can be produced by welding together the austenitic alloy base metalsaccording to any one of the present inventions (7) to (9) by variouswelding methods using any one of the welding materials for the primarypass welding and any one of the welding materials for the subsequentbuild-up passes to be used in producing the welded joint structuresaccording to any one of the present inventions (7) to (9). The weldedjoint structures of the present inventions (10) to (12) can be producedby welding together the austenitic alloy base metals according to anyone of the inventions (10) to (12) by various welding methods using anyone of the welding materials according to the present inventions (10) to(12).

In cases where high levels of corrosion resistance and creep strengthare required in the weld metal, it is not always necessary to form alllayers in the subsequent build-up passes of the multi-layer weldingusing the welding material according to any one of the presentinventions (7) to (12) but it is possible to carry out an intermediatelayer welding pass and the subsequent layer welding passes using acommercially available welding material properly selected, according tothe ratio of dilution from base metals, which influences the weldsolidification cracking. For example, in the case of welding where theratio of dilution from base metals is fairly low such as not more than20%, it may use a commercially available welding material, according tothe required levels of corrosion resistance and creep strength.

Further, in the case of welding thick base metals together, the weldingmaterials for the primary pass welding according to any one of theinventions (7) to (9) may be used not only in forming the primary layerbut also in forming the second and subsequent layers according to therequired level of ductility; thus, the welding material regulated foruse in the primary pass welding and the welding material regulated foruse in the subsequent build-up passes of the multi-layer welding may beused in combination in an appropriate manner.

While, in the case of similar material welding, the welding is carriedout using austenitic alloys having the “chemical composition 1” as basemetals, it is not always necessary that both the base metals areidentical in chemical composition; it is only required that they beaustenitic alloys respectively falling within the range of the “chemicalcomposition 1”. In the case of dissimilar material welding, the weldingmay be carried out using, as one of the base metals, an austenitic alloyhaving a composition falling within the range of the “chemicalcomposition 1” and, as the other base metal, an austenitic alloy havinga composition falling within the range of the “chemical composition 2”.Each base metal mentioned above may be an austenitic alloy which furthercontains, according to need, one or more elements selected from thefirst group and second group or both mentioned hereinabove.

(B) Penetration bead height of the weld metal in the welded jointstructure

The welded joint structures according to the present inventions (5) and(6) each has a penetration bead formed on the side opposite to the sidefrom which one side welding has been performed in the case of usingsheets as the base metals or, in the case of using tubular materials asthe base metals, on the inside of a tube as a result of circumferentialwelding from the outside of the tubular materials. In this case, thepenetration bead of the weld metal in each welded joint structure isrequired to have a height of 0 to 3 mm so that a level of strengthrequired of the welded joint structure can be ensured and a sound beadshape can be obtained.

When the penetration bead height is less than 0 mm, there is found theso-called “concave bead” where the bead surface is lower than thesurface opposite to the face on which the welding has been performed(interior surface in the case of a pipe); the strength of the weldedjoint structure thus becomes insufficient. On the other hand, apenetration bead height which exceeds 3 mm is unfavorable for ensuringstrength since the convex portion becomes excessively large and causesincreased stress concentration at the bead toe.

Therefore, the penetration bead height of the weld metal in the weldedjoint structure according to the present invention (5) or (6) is set to0 to 3 mm.

The chemical composition of the weld metal in each of theabove-mentioned welded joint structures should satisfy the requirementsgiven above in the section (A). Therefore, the welding material for usein the production of the above-mentioned welded joint structures is tobe selected according to the welding method and welding conditionsemployed so that the above-mentioned weld metal composition can beobtained.

However, when the welding is carried out using a welding materialdifferent in chemical composition from the base metals, the chemicalcomposition of the weld metal may be changed by dilution from the basemetals according to the welding conditions, such as welding heat input,groove shape and other multi-layer formation conditions. In particular,when the P content in the austenitic alloy base metals is high and morethan 0.03%, as in the case of the welded joint structure according tothe present invention (5) or (6), P flows into the weld metal toincrease the P content in the liquid phase, so that the susceptibilityto weld solidification cracking becomes high as compared with the caseof welding together base metals having an ordinary level P content notmore than 0.03%. Therefore, in order to inhibit weld solidificationcracking, it is recommended that the welding be carried out using ahigh-C and high-Cr content welding material at least in the primary passwelding and selecting the welding conditions so that at least thechemical composition of the weld metal in the primary layer may have acomposition falling within the range mentioned hereinabove.

Even when the conventional welding materials are used, it will betheoretically possible in certain cases to obtain a weld metal having achemical composition falling within the range mentioned above bysuppressing the ratio of dilution from the base metals to extremely lowlevels. However, in such a case, it becomes difficult to ensure a soundbead shape having a height within the above-mentioned range of 0 to 3mm.

The following examples illustrate the present invention morespecifically. These examples are, however, by no means limited to thescope of the present invention.

EXAMPLES Example 1

Austenitic alloys A to E, having the chemical compositions shown inTable 1, were melted using a high frequency induction vacuum furnace andthen cast to form ingots for use as base metals.

Both of the alloys A and E shown in Table 1 are austenitic alloys havingthe P content as high as 0.100%. On the other hand, the alloys B to Dare ordinary P content level austenitic alloys respectively having the Pcontents of 0.015%, 0.030% and 0.018%.

TABLE 1 Chemical composition (% by mass) The balance: Fe and impuritiesAlloy C Si Mn P S Cr Ni sol. Al N Others A 0.10 0.20 0.60 0.100 0.000518.12 8.86 0.026 0.009 Cu: 0.29, Nb: 0.21, Ti: 0.19 B 0.06 0.42 1.180.015 0.0010 25.07 19.90 0.021 0.250 Nb: 0.44, B: 0.0018 C 0.10 0.270.80 0.030 0.0002 18.10 9.30 0.025 0.094 Cu: 2.95, Nb: 0.42, Mo: 0.16 D0.08 0.22 0.60 0.018 0.0004 22.30 20.41 0.022 0.012 — E 0.39 0.21 0.820.100 0.0004 29.64 49.56 0.013 0.011 —

Austenitic alloys F to H, having the chemical compositions shown inTable 2, were melted using a high frequency induction vacuum furnace andthen cast to form ingots for use as welding materials.

The alloy G shown in Table 2 is an alloy whose C and Cr contents are outof the range which is regulated as the chemical composition of thewelding material by the present invention.

TABLE 2 Chemical composition (% by mass) The balance: Fe and impuritiesAlloy C Si Mn P S Cr Ni sol. Al N Others F 0.96 0.25 0.85 0.006 0.001029.45 60.39 0.002 0.005 — G *0.08   0.29 0.84 0.006 0.0010 *17.84  32.43 0.003 0.006 — H 0.99 0.22 0.63 0.006 0.0010 30.61 60.14 0.0340.005 Mo: 0.36, B: 0.0014 The mark * indicates falling outside theconditions regulated by the present invention.

Each ingot of the alloys A to E to be used as base metals was hot-forgedin the conventional manner and then subjected to a solution heattreatment at 1200° C., and then processed into restraint weld crackingtest specimens with a shape of U-groove (a butt thickness of 1.5 mm andan extension length of 2.5 mm) at the butt end and having a thickness of12 mm, a width of 50 mm and a length of 100 mm.

Each ingot of the alloys F to H was hot-forged in the conventionalmanner and then subjected to cold working with repetitions of solutionheat treatment before each cold working in order to obtain weldingmaterials each in the form of a wound wire having a diameter of 1.2 mm.

The thus-obtained restraint weld cracking test specimens wereperipherally restrained-welded; that is to say, using the saidspecimens, similar material welding (alloy A to alloy A and alloy E toalloy E) and dissimilar material welding (combinations of alloy A andalloy B, alloy A and alloy C, alloy A and alloy D, and alloy D and alloyE) were carried out in a peripherally restrained state.

Concretely, each butt site was subjected to primary pass welding usingany one of the above-mentioned welding materials F to H by the TIGwelding under the following conditions: welding current of 100 A,welding voltage of 12 V, and welding speed of 10 cm/min. In the saidwelding, the root gap was 0 mm, and three feeding speeds of the weldingmaterial, namely 48 cm/min, 54 cm/min and 62 cm/min, were employed tothereby vary the ratio of dilution from base metals.

After the said restraint welding, the weld bead surface in each specimenwas observed to determine whether the solidification cracking occurredor not.

Furthermore, five samples for sectional microstructure observation ofthe welded joint were taken from each test specimen. After mirror-likepolishing each surface of the said samples was examined to determinewhether the solidification cracking occurred or not, using an opticalmicroscope at a magnification of 500 times. After the said examination,the ratio of the area of the melted base metal portions to the area ofthe weld metal of the primary layer obtained by image analysis, namelythe ratio “(area of the melted base metal portions)/(area of the weldmetal of the primary layer)”, was calculated for each sample in order todetermine the average ratio of dilution from base metals of each saidtest specimen.

For each of the welded joint test specimens obtained by similar materialwelding, namely the welding of alloy A-to-alloy A or alloy E-to-alloy E,in which the austenitic alloys A and E had a high-P of 0.100%, thepenetration bead height was measured and the chemical composition of theobtained weld metal of the primary layer was analyzed, in addition tothe examinations mentioned hereinabove.

For each test specimen, the welding conditions, the average ratio ofdilution from base metals, the occurrence or nonoccurrence of beadsurface cracking and the incidence of weld solidification cracking inthe said five samples for sectional microstructure observation are shownin Table 3.

The penetration bead heights and the chemical compositions in the weldmetal of the primary layer, examined for each welded joint testspecimens obtained by similar material welding, namely the welding ofalloy A-to-alloy A or alloy E-to-alloy E, are shown in Table 4.

TABLE 3 Test Combination Feeding speed of Average ratio of dilution BeadWeld solidification cracking specimen of base Welding the weldingmaterial from base metals surface (Number of cracking)/(Number No.metals material (cm/min) (%) cracking of observed section) Note 1 A-A F48 63 free 0/5 Inventive 2 A-A F 54 59 free 0/5 Example 3 A-A F 62 51free 0/5 4 A-A H 50 60 free 0/5 5 A-B F 48 65 free 0/5 6 A-B F 54 60free 0/5 7 A-B F 62 50 free 0/5 8 A-C F 48 62 free 0/5 9 A-C F 54 59free 0/5 10 A-C F 62 53 free 0/5 11 A-B H 62 52 free 0/5 12 A-D F 62 51free 0/5 13 E-E F 59 55 free 0/5 14 D-E F 54 57 free 0/5 15 A-A * G 4862 occurred 5/5 Comparative 16 A-A * G 54 59 occurred 5/5 Example 17A-A * G 62 52 occurred 5/5 18 A-B * G 48 66 occurred 5/5 19 A-B * G 5461 occurred 5/5 20 A-B * G 62 50 occurred 5/5 21 A-C * G 48 61 occurred5/5 22 A-C * G 54 59 occurred 5/5 23 A-C * G 62 54 occurred 5/5 Themark * indicates falling outside the chemical compositions regulated bythe present invention.

TABLE 4 Weld metal of the primary layer Pene- Test tration spec- beadimen height Chemical composition (% by mass) The balance: Fe andimpurities No. (mm) C Si Mn P S Cr Ni sol.Al N Others Note 1 1.2 0.430.22 0.69 0.064 0.0007 22.43 28.44 0.017 0.008 Cu: 0.18, Nb: 0.13, Ti:0.12 Inven- 2 1.6 0.47 0.22 0.71 0.060 0.0007 22.99 31.02 0.016 0.007Cu: 0.17, Nb: 0.12, Ti: 0.11 tive 3 2.3 0.51 0.23 0.72 0.0550 0.0007023.56 33.59 0.0140. 0.007 Cu: 0.15, Nb: 0.11, Ti: 0.10 Example 13  2.00.65 0.23 0.83 .058 .0006 29.55 54.43 0.008 0.008 — # 15   1.4 * 0.09  0.23 0.69 0.065 0.0007 18.02 17.58 0.017 0.008 Cu: 0.18, Nb: 0.13, Ti:0.12 Com- # 16   1.6 * 0.09   0.24 0.71 0.059 0.0007 *17.99   19.230.016 0.008 Cu: 0.16, Nb: 0.12, Ti: 0.11 parative # 17   2.2 * 0.09  0.24 0.71 0.056 0.0007 *17.98   19.94 0.015 0.008 Cu: 0.15, Nb: 0.11,Ti: 0.10 Example The mark # indicates that the test specimens areobtained by welding using the welding material falling outside theconditions regulated by the present invention, and the mark * indicatesfalling outside the chemical compositions regulated by the presentinvention.

From Table 3, it is evident that no bead surface cracking was observedand no weld solidification cracking occurred in any of the testspecimens in Nos. 1 to 14, which were obtained by welding, using thewelding material F or H, satisfying the chemical compositionrequirements regulated by the present inventions (1) to (3),irrespective of whether they were products of similar material welding(alloy A to alloy A and alloy E to alloy E), or of dissimilar materialwelding (combinations of alloy A and alloy B, alloy A and alloy C, alloyA and alloy D, and alloy D and alloy E), even when the ratio of dilutionfrom base metals (average ratio of dilution from base metals) was high.

On the contrary, bead surface cracking was observed and the weldsolidification cracking was also found in all test specimens in Nos. 15to 23, which were obtained by welding, using the welding material G,having C and Cr contents less than those regulated by the presentinvention, irrespective of whether they were products of similarmaterial welding or of dissimilar material welding.

Further, from Table 4, it is evident that no weld solidificationcracking was observed in the test specimens in Nos. 1 to 3 and 13, wherethe chemical composition of the primary layer of the weld metal in oneside welding and the penetration bead height satisfied the respectiveconditions regulated by the present inventions (5) and (6); on the otherhand, in the test specimens in Nos. 15 to 17, where the chemicalcomposition of the primary layer of the weld metal in one side weldingdid not satisfy the condition regulated by the present inventions (5)and (6), weld solidification cracking was observed.

Example 2

Austenitic alloys D, E and I to L, having the chemical compositionsshown in Table 5, were melted using a high frequency induction vacuumfurnace and then cast to form ingots for use as base metals. In Table 5,the alloys D and E are the same alloys as melted in the above-mentioned“Example 1”.

Both of the alloys E and I shown in Table 5 are austenitic alloys havingthe P content as high as 0.100%. On the other hand, the alloys D and Jto L are ordinary P content level austenitic alloys respectively havingthe contents of P 0.018%, 0.010%, 0.015% and 0.028%.

TABLE 5 Chemical composition (% by mass) The balance: Fe and impuritiesAlloy C Si Mn P S Cr Ni sol.Al N Others D 0.08 0.22 0.60 0.018 0.000422.30 20.41 0.022 0.012 — E 0.39 0.21 0.82 0.100 0.0004 29.64 49.560.0130. 0.011 — I 0.10 0.26 0.54 0.100 0.0003 18.34 9.23 0.049 0.010 Nb:0.31, Ti: 0.20 J 0.08 0.21 1.12 0.010 0.0004 23.21 45.30 0.028 0.008 Nb:0.20, W: 7.13, B: 0.0040 K 0.06 0.40 1.15 0.015 0.0003 24.93 19.73 0.0060.223 Nb: 0.42, B: 0.0014 L 0.08 0.27 0.82 0.028 0.0003 18.12 8.98 0.0080.105 Cu: 2.98, Nb: 0.45, Mo: 0.16

Austenitic alloys F and M to P, having the chemical compositions shownin Table 6, were melted using a high frequency induction vacuum furnaceand then cast to form ingots for use as welding materials. The alloy Fin Table 6 is the same alloy as melted in the above-mentioned “Example1”.

The alloy M shown in Table 6 is an alloy whose C content is out of therange which is regulated as the chemical composition of the weldingmaterial by the present invention.

TABLE 6 Chemical composition (% by mass) The balance: Fe and impuritiesAlloy C Si Mn P S Cr Ni sol. Al N Others F 0.96 0.25 0.85 0.006 0.001029.45 60.39 0.0020. 0.005 — M *0.16   0.21 0.63 0.005 0.0003 30.71 59.960.026 0.005 B: 0.0018 M 0.29 0.23 0.68 0.005 0.0003 30.01 60.39 0.0240.005 B: 0.0030, W: 1.97 O 0.38 0.22 0.63 0.005 0.0003 30.72 60.28 0.0590.005 — P 0.99 0.22 0.63 0.006 0.0003 30.61 60.14 0.034 0.006 B: 0.0014The mark * indicates falling outside the conditions regulated by thepresent invention.

Each ingot of the alloys D, E and I to L to be used as base metals werehot-forged in the conventional manner and then subjected to a solutionheat treatment at 1150° C., hollowed out in the center by machining andthen processed into tubular restraint weld cracking test specimens withshapes of U-groove (a butt thickness of 1.5 mm and an extension lengthof 2.5 mm) and V-groove (a butt thickness of 1.0 mm and an angle of 60°)at the butt end and having a thickness of 9 mm, an outside diameter of40 mm and a length of 50 mm.

Each ingot of the alloys F and M to P was hot-forged in the conventionalmanner and then subjected to cold working with repetitions of solutionheat treatment before each cold working in order to obtain weldingmaterials each in the form of a solid wire having a diameter of 2.0 mmor a wound wire having a diameter of 1.2 mm.

The thus-obtained tubular restraint weld cracking test specimens wereperipherally restrained-welded with a rod inserted, as shown in FIG. 1;that is to say, using the said specimens, similar material welding(alloy I to alloy I and alloy E to alloy E) and dissimilar materialwelding (combinations of alloy I and alloy J, alloy I and alloy K, alloyI and alloy L, and alloy D and alloy E) were carried out in aperipherally restrained state.

Concretely, each butt site of U-grooves and V-grooves was subjected to aprimary pass welding using any one of the above-mentioned weldingmaterials F and M to P.

In the case of the V-groove welding, the welding was carried out by TIGwelding under the following conditions: welding current of 100 A,welding voltage of 12 V, and welding speed of 8 cm/min. In the case ofthe U-groove welding, the welding was carried out by TIG welding underthe following conditions: welding current of 110 A, welding voltage of12 V, and welding speed of 8 cm/min. The ratio of dilution from basemetals was varied by changing the groove shape, root gap and feedingspeed of welding materials.

After the said primary pass welding by TIG welding, the weld beadsurface in each tubular specimen was observed to determine whethersolidification cracking occurred or not.

Furthermore, five samples for sectional microstructure observation ofthe welded joint were taken from each primary pass welded test specimen.After mirror-like polishing each surface of the said samples wasexamined to determine whether the solidification cracking occurred ornot, using an optical microscope at a magnification of 500 times. Afterthe said examination, the ratio of the area of the melted base metalportions to the area of the weld metal of the primary layer obtained byimage analysis, namely the ratio “(area of the melted base metalportions)/(area of the weld metal of the primary layer)”, was calculatedfor each sample in order to determine the average ratio of dilution frombase metals of each said test specimen.

For each test specimen, the welding conditions, the average ratio ofdilution from base metals, the occurrence or nonoccurrence of beadsurface cracking and the incidence of weld solidification cracking inthe said five samples for sectional microstructure observation are shownin Table 7.

TABLE 7 Test Combination Shape Root Average ratio of dilution Bead Weldsolidification cracking specimen of base of Welding gap from base metalssurface (Number of cracking)/(Number No. metals grove material (mm) (%)cracking of observed section) 24 I-I U M 0 68 occurred 5/5 25 I-I U P 061 free 0/5 26 I-I V M 2 32 occurred 5/5 27 I-I V N 2 33 free 0/5 28 I-IV P 1 39 free 0/5 29 I-J U N 0 70 occurred 5/5 30 I-J U P 0 66 free 0/531 I-J V O 2 28 free 0/5 32 I-J V P 2 46 free 0/5 33  I-K U M 0 63occurred 5/5 34  I-K U P 0 61 free 0/5 35  I-K V O 2 30 free 0/5 36  I-KV P 2 38 free 0/5 37  I-L U N 0 68 occurred 5/5 38  I-L U P 0 59 free0/5 39  I-L V O 2 29 free 0/5 40  I-L V P 2 31 free 0/5 41 D-E  U F 0 58free 0/5 42 D-E  V F 2 33 free 0/5 43 E-E U F 0 61 free 0/5 44 E-E V F 235 free 0/5

As is apparent from Table 7, the test specimens in Nos. 25, 27, 28, 30to 32, 34 to 36 and 38 to 44 showed no bead surface cracking and no weldsolidification cracking.

On the other hand, bead surface cracking was observed and the weldsolidification cracking was also found in all test specimens in Nos. 24,26, 29, 33 and 37.

From the results mentioned above, it is seen that the test specimens inNos. 24, 26 and 33, which showed the ratios of dilution from base metalsof 68%, 32% and 63%, respectively, failed to counteract the malignantinfluence of the inflow of P from the base metals and allowedsolidification cracking to occur in the weld metal of the primary layer,irrespective of the ratio of dilution from base metals, since the Ccontent of the alloy M, used as the welding material was 0.16% which wasoutside the lower limit of the C content range regulated by the presentinvention.

It is also seen that the test specimens in Nos. 29 and 37, which showedhigh ratios of dilution from base metals of 70% and 68% respectively,and therefore large amounts of inflow of P occurred, but the C contentof the alloy N used as the welding material was as low as 0.29%; hencethe said test specimens failed to counteract the malignant influence ofthe inflow of P from the base metals and allowed solidification crackingto occur in the weld metal of the primary layer. In the test specimen inNo. 27 obtained by welding using the same alloy N as the weldingmaterial at a ratio of dilution from base metals of lower than 50%, theinflow of P was suppressed and no weld solidification cracking wasobserved.

Therefore, those welded joints produced by the primary pass weldingunder the same conditions as shown in the above-mentioned Table 7, whichshowed no weld solidification cracking in the weld metal of the primarylayer, were subjected to build-up pass welding using the weldingmaterials F and M to P in such a combination as shown in Tables 8 and 9by the TIG welding under the following conditions: welding current of130 A, welding voltage of 12 V, and welding speed of 10 cm/min.

TABLE 8 Test Combination Shape Welding material Root Average ratio ofdilution Welding material Weld solidification cracking Bend specimen ofbase of for primary gap from base metals for build-up (Number ofcracking)/(Number test No. metals grove pass welding (mm) (%) passwelding of observed section) result 25-1 I-I U P 0 61 M 4/5 x 25-2 I-I UP 0 61 N 0/5 ∘ 25-3 I-I U P 0 61 O 0/5 ∘ 25-4 I-I U P 0 61 P 0/5 Δ 27-1I-I V N 2 33 O 0/5 ∘ 27-2 I-I V N 2 33 P 0/5 Δ 28-1 I-I V P 1 39 M 3/5 x28-2 I-I V P 1 39 O 0/5 ∘ 28-3 I-I V P 1 39 P 0/5 Δ 30-1 I-J U P 0 66 N0/5 ∘ 30-2 I-J U P 0 66 O 0/5 ∘ 30-3 I-J U P 0 66 P 0/5 Δ 31-1 I-J V O 228 O 0/5 ∘ 31-2 I-J V O 2 28 P 0/5 Δ 32-1 I-J V P 2 46 N 0/5 ∘ 32-2 I-JV P 2 46 P 0/5 Δ 34-1  I-K U P 0 61 M 4/5 x 34-2  I-K U P 0 61 P 0/5 Δ35-1  I-K V O 2 30 N 0/5 ∘ 35-2  I-K V O 2 30 O 0/5 ∘

TABLE 9 Test Combination Shape Welding material Root Average ratio ofdilution Welding material Weld solidification cracking Bend specimen ofbase of for primary gap from base metals for build-up (Number ofcracking)/(Number test No. metals grove pass welding (mm) (%) passwelding of observed section) result 36-1  I-K V P 2 38 O 0/5 ∘ 36-2  I-KV P 2 38 P 0/5 Δ 38-1 I-L U P 0 59 M 4/5 x 38-2 I-L U P 0 59 O 0/5 ∘38-3 I-L U P 0 59 P 0/5 Δ 39-1 I-L V O 2 29 O 0/5 ∘ 39-2 I-L V O 2 29 P0/5 Δ 40-1 I-L V P 2 31 O 0/5 ∘ 40-2 I-L V P 2 31 P 0/5 Δ 41-1 D-E  U F0 58 F 0/5 Δ 41-2 D-E  U F 0 58 O 0/5 ∘ 42-1 D-E  V F 2 33 F 0/5 Δ 42-2D-E  V F 2 33 O 0/5 ∘ 43-1 E-E  U F 0 61 F 0/5 Δ 43-2 E-E  U F 0 61 O0/5 ∘ 44-1 E-E  V F 2 35 F 0/5 Δ 44-2 E-E  V F 2 35 O 0/5 ∘

Five samples for sectional microstructure observation of the weldedjoint were taken from each build-up pass welded test specimen. Aftermirror-like polishing each build-up pass welded portion of the saidsamples was examined to determine whether the solidification crackingoccurred or not, using an optical microscope at a magnification of 500times. Further, two samples having a 3-mm-thick for a lateral bend testwere taken from each welded joint test specimen showing no weldsolidification cracking in the build-up pass welded portion and weresubjected to a bend test at a bending radius of R of 6 mm.

For each build-up pass welded test specimen, the incidence of weldsolidification cracking in the said five samples for sectionalmicrostructure observation and the results of the said bend test arecollectively shown in Tables 8 and 9. The mark “∘” in the column “Resultof bend test” in Tables 8 and 9 indicates that the 180°-bending waspossible in each lateral bend test of the two samples and no crackopening was observed after the said bend test. On the other hand, themark “A” indicates that the 180°-bending was possible in each lateralbend test of the two samples but crack openings, including microcracks,were observed after the said bend test. Further, the mark “x” indicatesthat, in at least one of the two samples, the 180°-bending wasimpossible in the lateral bend test and breakage occurred during thesaid bend test.

As can be seen from Tables 8 and 9, no weld solidification cracking wasobserved in the build-up pass welded portion, the results of the bendtest were good, the 180°-bending could be performed and no crack openingwas found after the said bend test in the said test specimens in Nos.25-2, 25-3, 27-1, 28-2, 30-1, 30-2, 31-1, 32-1, 35-1, 35-2, 36-1, 38-2,39-1, 40-1, 41-2, 42-2, 43-2 and 44-2.

On the contrary, it was revealed that, in the case of the test specimensin Nos. 25-1, 28-1, 34-1 and 38-1, where the C content of the alloy M,used as the welding material in the build-up pass welding was as low as0.16% and outside the C content range regulated herein for all weldingmaterials according to the present invention, the malignant influence ofthe inflow of P could not be counteracted, therefore weld solidificationcracking occurred in the build-up pass welded portion. Furthermore,crack openings accompanying the weld solidification cracking were foundin the bend testing, and the results of the said bend test were alsoinferior.

It was further found that, in the case of the test specimens in Nos.25-4, 27-2, 28-3, 30-3, 31-2, 32-2, 34-2, 36-2, 38-3, 39-2 and 40-2,where the C content of the welding material P, used as the build-up passwelding material was higher than the range regulated herein according tothe present inventions (7) to (10), the amounts of eutectic carbideprecipitates formed in the build-up pass welded portion increased and,as a result, the ductility deteriorated, giving inferior results in thesaid bend test.

Similarly, it was also revealed that, in the case of the test specimensin Nos. 41-1, 42-1, 43-1 and 44-1, where the C content of the weldingmaterial F, used as the build-up pass welding material was higher thanthe amounts regulated herein according to the present inventions (10) to(12), the amounts of eutectic carbide precipitates formed in thebuild-up pass welded portion increased and, as a result, the ductilitydeteriorated, giving inferior results in the said bend test.

INDUSTRIAL APPLICABILITY

The welding materials of the present invention, in spite of at least oneof the base metals has a high P content of more than 0.03% to not morethan 0.3% and shows fully austenitic solidification, can suppress weldsolidification cracking; therefore, they can be widely used in suchfields where a welding fabrication is required. Furthermore, the weldedjoint structures of the present invention, in spite of at least one ofthe base metals has a high P content mentioned above and shows fullyaustenitic solidification, are excellent in weld solidification crackingresistance or in both weld solidification cracking resistance andductility. In addition, the welded joint structures of the presentinvention also have excellent high temperature strength and corrosionresistance. The welding materials of the present invention are bestsuited for producing the above-mentioned austenitic alloy welded jointstructures.

1. A welding material to be used for welding a base metal made of anaustenitic alloy having the following “chemical composition 21” to abase metal made of another austenitic alloy, comprising: by masspercent, C: 0.8 to 3.0%, Si: not more than 4.0%, Mn: not more than 3.0%,P: not more than 0.03%, S: not more than 0.03%, Cr: more than 22% to notmore than 55%, Ni: more than 30% to not more than 70%, sol. Al: 0.001 to1% and N: not more than 0.3%, with the balance being Fe and impurities:“Chemical composition 21”: a chemical composition which comprises, bymass percent, C: not more than 2.0%, Si: not more than 4.0%, Mn: 0.01 to3.0%, P: more than 0.03% to not more than 0.3%, S: not more than 0.03%,Cr: 12 to 35%, Ni: 6 to 80%, sol. Al: 0.001 to 5%, N: not more than 0.3%and one or more elements selected from Ca: not more than 0.05%, Mg: notmore than 0.05% and REM: not more than 0.3%, with the balance being Feand impurities.
 2. The welding material according to claim 1, in whichthe base metal made of the another austenitic alloy has the following“chemical composition 21”: “Chemical composition 21”: a chemicalcomposition which comprises, by mass percent, C: not more than 2.0%, Si:not more than 4.0%, Mn: 0.01 to 3.0%, P: more than 0.03% to not morethan 0.3%, S: not more than 0.03%, Cr: 12 to 35%, Ni: 6 to 80%, sol. Al:0.001 to 5%, N: not more than 0.3% and one or more elements selectedfrom Ca: not more than 0.05%, Mg: not more than 0.05% and REM: not morethan 0.3%, with the balance being Fe and impurities.
 3. The weldingmaterial according to claim 1, in which one or more alloys among thebase metals and welding material contain one or more elements selectedfrom the first group given below in lieu of a part of Fe, by masspercent: first group: Cu: not more than 5%, Mo: not more than 10%, W:not more than 10%, V: not more than 2%, Nb: not more than 3%, Ti: notmore than 3%, Ta: not more than 8%, Zr: not more than 1%, Hf: not morethan 1%, Co: not more than 15% and B: not more than 0.03%.
 4. Thewelding material according to claim 2, in which one or more alloys amongthe base metals and welding material contain one or more elementsselected from the first group given below in lieu of a part of Fe, bymass percent: first group: Cu: not more than 5%, Mo: not more than 10%,W: not more than 10%, V: not more than 2%, Nb: not more than 3%, Ti: notmore than 3%, Ta: not more than 8%, Zr: not more than 1%, Hf: not morethan 1%, Co: not more than 15% and B: not more than 0.03%.
 5. A weldedjoint structure in which a base metal made of an austenitic alloy havingthe following “chemical composition 22” is welded to a base metal madeof another austenitic alloy by using the welding material comprising, bymass percent, C: more than 0.3% to not more than 3.0%, Si: not more than4.0%, Mn: not more than 3.0%, P: not more than 0.03%, S: not more than0.03%, Cr: more than 22% to not more than 55%, Ni: more than 30% to notmore than 70%, sol. Al: 0.001 to 1% and N: not more than 0.3%, with thebalance being Fe and impurities: “Chemical composition 22”: a chemicalcomposition which comprises, by mass percent, C: not more than 2.0%, Si:not more than 4.0%, Mn: 0.01 to 3.0%, P: more than 0.08% to not morethan 0.3%, S: not more than 0.03%, Cr: 12 to 35%, Ni: 6 to 80%, sol. Al:0.001 to 5%, N: not more than 0.3% and one or more elements selectedfrom Ca: not more than 0.05%, Mg: not more than 0.05% and REM: not morethan 0.3%, with the balance being Fe and impurities.
 6. The welded jointstructure according to claim 5 in which the base metal made of theanother austenitic alloy has the following “chemical composition 22”:“Chemical composition 22”: a chemical composition which comprises, bymass percent, C: not more than 2.0%, Si: not more than 4.0%, Mn: 0.01 to3.0%, P: more than 0.08% to not more than 0.3%, S: not more than 0.03%,Cr: 12 to 35%, Ni: 6 to 80%, sol. Al: 0.001 to 5%, N: not more than 0.3%and one or more elements selected from Ca: not more than 0.05%, Mg: notmore than 0.05% and REM: not more than 0.3%, with the balance being Feand impurities.
 7. The welded joint structure according to claim 5, inwhich one or more alloys among the base metals and welding materialcontain one or more elements selected from the first group given belowin lieu of a part of Fe, by mass percent: first group: Cu: not more than5%, Mo: not more than 10%, W: not more than 10%, V: not more than 2%,Nb: not more than 3%, Ti: not more than 3%, Ta: not more than 8%, Zr:not more than 1%, Hf: not more than 1%, Co: not more than 15% and B: notmore than 0.03%.
 8. The welded joint structure according to claim 6, inwhich one or more alloys among the base metals and welding materialcontain one or more elements selected from the first group given belowin lieu of a part of Fe, by mass percent: first group: Cu: not more than5%, Mo: not more than 10%, W: not more than 10%, V: not more than 2%,Nb: not more than 3%, Ti: not more than 3%, Ta: not more than 8%, Zr:not more than 1%, Hf: not more than 1%, Co: not more than 15% and B: notmore than 0.03%.
 9. A welded joint structure which is constructed withbase metals each made of an austenitic alloy comprising, by masspercent, C: not more than 2.0%, Si: not more than 4.0%, Mn: 0.01 to3.0%, P: more than 0.08% to not more than 0.3%, S: not more than 0.03%,Cr: 12 to 35%, Ni: 6 to 80%, sol. Al: 0.001 to 5%, N: not more than 0.3%and one or more elements selected from Ca: not more than 0.05%, Mg: notmore than 0.05% and REM: not more than 0.3%, with the balance being Feand impurities, and a weld metal made of an austenitic alloy having thefollowing characteristics (i) and (ii): (i) the chemical composition ofat least the primary layer being welded from one side, comprises, bymass percent, C: more than 0.1% to not more than 0.7%, Si: not more than4.0%, Mn: not more than 3.0%, P: more than 0.03% to not more than 0.1%,S: not more than 0.03%, Cr: 18 to 30%, Ni: more than 10% to not morethan 70%, sol. Al: 0.001 to 1% and N: not more than 0.3%, with thebalance being Fe and impurities; and (ii) the penetration bead has aheight of 0 to 3 mm.
 10. The welded joint structure according to claim9, in which one or more alloys among the base metals and weld metalcontain one or more elements selected from the first group given belowin lieu of a part of Fe, by mass percent: first group: Cu: not more than5%, Mo: not more than 10%, W: not more than 10%, V: not more than 2%,Nb: not more than 3%, Ti: not more than 3%, Ta: not more than 8%, Zr:not more than 1%, Hf: not more than 1%, Co: not more than 15% and B: notmore than 0.03%.
 11. A welded joint structure resulting from welding ofa base metal made of an austenitic alloy having the following “chemicalcomposition 22” to a base metal made of another austenitic alloy, on theoccasion of welding, a welding material which comprises, by masspercent, C: more than 0.6% to not more than 2.0%, Si: not more than4.0%, Mn: not more than 3.0%, P: not more than 0.03%, S: not more than0.03%, Cr: more than 22% to not more than 35%, Ni: more than 30% to notmore than 70%, sol. Al: 0.001 to 1% and N: not more than 0.3%, with thebalance being Fe and impurities, is used in the primary pass of themulti-layer welding and a welding material which comprises, by masspercent, C: more than 0.2% to not more than 0.6%, Si: not more than4.0%, Mn: not more than 3.0%, P: not more than 0.03%, S: not more than0.03%, Cr: more than 22% to not more than 35%, Ni: more than 30% to notmore than 70%, sol. Al: 0.001 to 1% and N: not more than 0.3%, with thebalance being Fe and impurities, is used in the subsequent build-uppasses of the said multi-layer welding: “Chemical composition 22”: achemical composition which comprises, by mass percent, C: not more than2.0%, Si: not more than 4.0%, Mn: 0.01 to 3.0%, P: more than 0.08% tonot more than 0.3%, S: not more than 0.03%, Cr: 12 to 35%, Ni: 6 to 80%,sol. Al: 0.001 to 5%, N: not more than 0.3% and one or more elementsselected from Ca: not more than 0.05%, Mg: not more than 0.05% and REM:not more than 0.3%, with the balance being Fe and impurities.
 12. Thewelded joint structure according to claim 11, in which the base metalmade of the another austenitic alloy has the following “chemicalcomposition 22”: “Chemical composition 22”: a chemical composition whichcomprises, by mass percent, C: not more than 2.0%, Si: not more than4.0%, Mn: 0.01 to 3.0%, P: more than 0.08% to not more than 0.3%, S: notmore than 0.03%, Cr: 12 to 35%, Ni: 6 to 80%, sol. Al: 0.001 to 5%, N:not more than 0.3% and one or more elements selected from Ca: not morethan 0.05%, Mg: not more than 0.05% and REM: not more than 0.3%, withthe balance being Fe and impurities.
 13. The welded joint structureaccording to claim 11, in which one or more alloys among the base metalsand welding material contain one or more elements selected from thefirst group given below in lieu of a part of Fe, by mass percent: firstgroup: Cu: not more than 5%, Mo: not more than 10%, W: not more than10%, V: not more than 2%, Nb: not more than 3%, Ti: not more than 3%,Ta: not more than 8%, Zr: not more than 1%, Hf: not more than 1%, Co:not more than 15% and B: not more than 0.03%.
 14. The welded jointstructure according to claim 12, in which one or more alloys among thebase metals and welding material contain one or more elements selectedfrom the first group given below in lieu of a part of Fe, by masspercent: first group: Cu: not more than 5%, Mo: not more than 10%, W:not more than 10%, V: not more than 2%, Nb: not more than 3%, Ti: notmore than 3%, Ta: not more than 8%, Zr: not more than 1%, Hf: not morethan 1%, Co: not more than 15% and B: not more than 0.03%.
 15. A weldedjoint structure resulting from welding of a base metal made of anaustenitic alloy having the following “chemical composition 22” to abase metal made of another austenitic alloy, on the occasion of welding,using a welding material which comprises by mass percent, C: more than0.2% to not more than 0.6%, Si: not more than 4.0%, Mn: not more than3.0%, P: not more than 0.03%, S: not more than 0.03%, Cr: more than 22%to not more than 35%, Ni: more than 30% to not more than 70%, sol. Al:0.001 to 1% and N: not more than 0.3%, with the balance being Fe andimpurities, at least the welding of the primary layer is carried outunder a condition such that the ratio of dilution from the base metalsbecomes less than 50%: “Chemical composition 22”: a chemical compositionwhich comprises, by mass percent, C: not more than 2.0%, Si: not morethan 4.0%, Mn: 0.01 to 3.0%, P: more than 0.03% 0.08% to not more than0.3%, S: not more than 0.03%, Cr: 12 to 35%, Ni: 6 to 80%, sol. Al:0.001 to 5%, N: not more than 0.3% and one or more elements selectedfrom Ca: not more than 0.05%, Mg: not more than 0.05% and REM: not morethan 0.3%, with the balance being Fe and impurities.
 16. The weldedjoint structure according to claim 15, in which the base metal made ofthe another austenitic alloy has the following “chemical composition22”: “Chemical composition 22”: a chemical composition which comprises,by mass percent, C: not more than 2.0%, Si: not more than 4.0%, Mn: 0.01to 3.0%, P: more than 0.08% to not more than 0.3%, S: not more than0.03%, Cr: 12 to 35%, Ni: 6 to 80%, sol. Al: 0.001 to 5%, N: not morethan 0.3% and one or more elements selected from Ca: not more than0.05%, Mg: not more than 0.05% and REM: not more than 0.3%, with thebalance being Fe and impurities.
 17. The welded joint structureaccording to claim 15, in which one or more alloys among the base metalsand welding material contain one or more elements selected from thefirst group given below in lieu of a part of Fe, by mass percent: firstgroup: Cu: not more than 5%, Mo: not more than 10%, W: not more than10%, V: not more than 2%, Nb: not more than 3%, Ti: not more than 3%,Ta: not more than 8%, Zr: not more than 1%, Hf: not more than 1%, Co:not more than 15% and B: not more than 0.03%.
 18. The welded jointstructure according to claim 16, in which one or more alloys among thebase metals and welding material contain one or more elements selectedfrom the first group given below in lieu of a part of Fe, by masspercent: first group: Cu: not more than 5%, Mo: not more than 10%, W:not more than 10%, V: not more than 2%, Nb: not more than 3%, Ti: notmore than 3%, Ta: not more than 8%, Zr: not more than 1%, Hf: not morethan 1%, Co: not more than 15% and B: not more than 0.03%.